path: root/devdocs/python~3.12/library%2Fast.html

 <span id="ast-abstract-syntax-trees"></span><h1>ast — Abstract Syntax Trees</h1> <p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.12/Lib/ast.py">Lib/ast.py</a></p>  <p>The <a class="reference internal" href="#module-ast" title="ast: Abstract Syntax Tree classes and manipulation."><code>ast</code></a> module helps Python applications to process trees of the Python abstract syntax grammar. The abstract syntax itself might change with each Python release; this module helps to find out programmatically what the current grammar looks like.</p> <p>An abstract syntax tree can be generated by passing <a class="reference internal" href="#ast.PyCF_ONLY_AST" title="ast.PyCF_ONLY_AST"><code>ast.PyCF_ONLY_AST</code></a> as a flag to the <a class="reference internal" href="functions#compile" title="compile"><code>compile()</code></a> built-in function, or using the <a class="reference internal" href="#ast.parse" title="ast.parse"><code>parse()</code></a> helper provided in this module. The result will be a tree of objects whose classes all inherit from <a class="reference internal" href="#ast.AST" title="ast.AST"><code>ast.AST</code></a>. An abstract syntax tree can be compiled into a Python code object using the built-in <a class="reference internal" href="functions#compile" title="compile"><code>compile()</code></a> function.</p> <section id="abstract-grammar"> <span id="id1"></span><h2>Abstract Grammar</h2> <p>The abstract grammar is currently defined as follows:</p> <pre data-language="asdl">-- ASDL's 4 builtin types are:
-- identifier, int, string, constant

module Python
{
    mod = Module(stmt* body, type_ignore* type_ignores)
        | Interactive(stmt* body)
        | Expression(expr body)
        | FunctionType(expr* argtypes, expr returns)

    stmt = FunctionDef(identifier name, arguments args,
                       stmt* body, expr* decorator_list, expr? returns,
                       string? type_comment, type_param* type_params)
          | AsyncFunctionDef(identifier name, arguments args,
                             stmt* body, expr* decorator_list, expr? returns,
                             string? type_comment, type_param* type_params)

          | ClassDef(identifier name,
             expr* bases,
             keyword* keywords,
             stmt* body,
             expr* decorator_list,
             type_param* type_params)
          | Return(expr? value)

          | Delete(expr* targets)
          | Assign(expr* targets, expr value, string? type_comment)
          | TypeAlias(expr name, type_param* type_params, expr value)
          | AugAssign(expr target, operator op, expr value)
          -- 'simple' indicates that we annotate simple name without parens
          | AnnAssign(expr target, expr annotation, expr? value, int simple)

          -- use 'orelse' because else is a keyword in target languages
          | For(expr target, expr iter, stmt* body, stmt* orelse, string? type_comment)
          | AsyncFor(expr target, expr iter, stmt* body, stmt* orelse, string? type_comment)
          | While(expr test, stmt* body, stmt* orelse)
          | If(expr test, stmt* body, stmt* orelse)
          | With(withitem* items, stmt* body, string? type_comment)
          | AsyncWith(withitem* items, stmt* body, string? type_comment)

          | Match(expr subject, match_case* cases)

          | Raise(expr? exc, expr? cause)
          | Try(stmt* body, excepthandler* handlers, stmt* orelse, stmt* finalbody)
          | TryStar(stmt* body, excepthandler* handlers, stmt* orelse, stmt* finalbody)
          | Assert(expr test, expr? msg)

          | Import(alias* names)
          | ImportFrom(identifier? module, alias* names, int? level)

          | Global(identifier* names)
          | Nonlocal(identifier* names)
          | Expr(expr value)
          | Pass | Break | Continue

          -- col_offset is the byte offset in the utf8 string the parser uses
          attributes (int lineno, int col_offset, int? end_lineno, int? end_col_offset)

          -- BoolOp() can use left &amp; right?
    expr = BoolOp(boolop op, expr* values)
         | NamedExpr(expr target, expr value)
         | BinOp(expr left, operator op, expr right)
         | UnaryOp(unaryop op, expr operand)
         | Lambda(arguments args, expr body)
         | IfExp(expr test, expr body, expr orelse)
         | Dict(expr* keys, expr* values)
         | Set(expr* elts)
         | ListComp(expr elt, comprehension* generators)
         | SetComp(expr elt, comprehension* generators)
         | DictComp(expr key, expr value, comprehension* generators)
         | GeneratorExp(expr elt, comprehension* generators)
         -- the grammar constrains where yield expressions can occur
         | Await(expr value)
         | Yield(expr? value)
         | YieldFrom(expr value)
         -- need sequences for compare to distinguish between
         -- x &lt; 4 &lt; 3 and (x &lt; 4) &lt; 3
         | Compare(expr left, cmpop* ops, expr* comparators)
         | Call(expr func, expr* args, keyword* keywords)
         | FormattedValue(expr value, int conversion, expr? format_spec)
         | JoinedStr(expr* values)
         | Constant(constant value, string? kind)

         -- the following expression can appear in assignment context
         | Attribute(expr value, identifier attr, expr_context ctx)
         | Subscript(expr value, expr slice, expr_context ctx)
         | Starred(expr value, expr_context ctx)
         | Name(identifier id, expr_context ctx)
         | List(expr* elts, expr_context ctx)
         | Tuple(expr* elts, expr_context ctx)

         -- can appear only in Subscript
         | Slice(expr? lower, expr? upper, expr? step)

          -- col_offset is the byte offset in the utf8 string the parser uses
          attributes (int lineno, int col_offset, int? end_lineno, int? end_col_offset)

    expr_context = Load | Store | Del

    boolop = And | Or

    operator = Add | Sub | Mult | MatMult | Div | Mod | Pow | LShift
                 | RShift | BitOr | BitXor | BitAnd | FloorDiv

    unaryop = Invert | Not | UAdd | USub

    cmpop = Eq | NotEq | Lt | LtE | Gt | GtE | Is | IsNot | In | NotIn

    comprehension = (expr target, expr iter, expr* ifs, int is_async)

    excepthandler = ExceptHandler(expr? type, identifier? name, stmt* body)
                    attributes (int lineno, int col_offset, int? end_lineno, int? end_col_offset)

    arguments = (arg* posonlyargs, arg* args, arg? vararg, arg* kwonlyargs,
                 expr* kw_defaults, arg? kwarg, expr* defaults)

    arg = (identifier arg, expr? annotation, string? type_comment)
           attributes (int lineno, int col_offset, int? end_lineno, int? end_col_offset)

    -- keyword arguments supplied to call (NULL identifier for **kwargs)
    keyword = (identifier? arg, expr value)
               attributes (int lineno, int col_offset, int? end_lineno, int? end_col_offset)

    -- import name with optional 'as' alias.
    alias = (identifier name, identifier? asname)
             attributes (int lineno, int col_offset, int? end_lineno, int? end_col_offset)

    withitem = (expr context_expr, expr? optional_vars)

    match_case = (pattern pattern, expr? guard, stmt* body)

    pattern = MatchValue(expr value)
            | MatchSingleton(constant value)
            | MatchSequence(pattern* patterns)
            | MatchMapping(expr* keys, pattern* patterns, identifier? rest)
            | MatchClass(expr cls, pattern* patterns, identifier* kwd_attrs, pattern* kwd_patterns)

            | MatchStar(identifier? name)
            -- The optional "rest" MatchMapping parameter handles capturing extra mapping keys

            | MatchAs(pattern? pattern, identifier? name)
            | MatchOr(pattern* patterns)

             attributes (int lineno, int col_offset, int end_lineno, int end_col_offset)

    type_ignore = TypeIgnore(int lineno, string tag)

    type_param = TypeVar(identifier name, expr? bound)
               | ParamSpec(identifier name)
               | TypeVarTuple(identifier name)
               attributes (int lineno, int col_offset, int end_lineno, int end_col_offset)
}
</pre> </section> <section id="node-classes"> <h2>Node classes</h2> <dl class="py class"> <dt class="sig sig-object py" id="ast.AST">
<code>class ast.AST</code> </dt> <dd>
<p>This is the base of all AST node classes. The actual node classes are derived from the <code>Parser/Python.asdl</code> file, which is reproduced <a class="reference internal" href="#abstract-grammar"><span class="std std-ref">above</span></a>. They are defined in the <code>_ast</code> C module and re-exported in <a class="reference internal" href="#module-ast" title="ast: Abstract Syntax Tree classes and manipulation."><code>ast</code></a>.</p> <p>There is one class defined for each left-hand side symbol in the abstract grammar (for example, <code>ast.stmt</code> or <code>ast.expr</code>). In addition, there is one class defined for each constructor on the right-hand side; these classes inherit from the classes for the left-hand side trees. For example, <a class="reference internal" href="#ast.BinOp" title="ast.BinOp"><code>ast.BinOp</code></a> inherits from <code>ast.expr</code>. For production rules with alternatives (aka “sums”), the left-hand side class is abstract: only instances of specific constructor nodes are ever created.</p> <span class="target" id="index-0"></span><span class="target" id="index-1"></span><dl class="py attribute"> <dt class="sig sig-object py" id="ast.AST._fields">
<code>_fields</code> </dt> <dd>
<p>Each concrete class has an attribute <a class="reference internal" href="#ast.AST._fields" title="ast.AST._fields"><code>_fields</code></a> which gives the names of all child nodes.</p> <p>Each instance of a concrete class has one attribute for each child node, of the type as defined in the grammar. For example, <a class="reference internal" href="#ast.BinOp" title="ast.BinOp"><code>ast.BinOp</code></a> instances have an attribute <code>left</code> of type <code>ast.expr</code>.</p> <p>If these attributes are marked as optional in the grammar (using a question mark), the value might be <code>None</code>. If the attributes can have zero-or-more values (marked with an asterisk), the values are represented as Python lists. All possible attributes must be present and have valid values when compiling an AST with <a class="reference internal" href="functions#compile" title="compile"><code>compile()</code></a>.</p> </dd>
</dl> <dl class="py attribute"> <dt class="sig sig-object py" id="ast.AST.lineno">
<code>lineno</code> </dt> <dt class="sig sig-object py" id="ast.AST.col_offset">
<code>col_offset</code> </dt> <dt class="sig sig-object py" id="ast.AST.end_lineno">
<code>end_lineno</code> </dt> <dt class="sig sig-object py" id="ast.AST.end_col_offset">
<code>end_col_offset</code> </dt> <dd>
<p>Instances of <code>ast.expr</code> and <code>ast.stmt</code> subclasses have <a class="reference internal" href="#ast.AST.lineno" title="ast.AST.lineno"><code>lineno</code></a>, <a class="reference internal" href="#ast.AST.col_offset" title="ast.AST.col_offset"><code>col_offset</code></a>, <a class="reference internal" href="#ast.AST.end_lineno" title="ast.AST.end_lineno"><code>end_lineno</code></a>, and <a class="reference internal" href="#ast.AST.end_col_offset" title="ast.AST.end_col_offset"><code>end_col_offset</code></a> attributes. The <a class="reference internal" href="#ast.AST.lineno" title="ast.AST.lineno"><code>lineno</code></a> and <a class="reference internal" href="#ast.AST.end_lineno" title="ast.AST.end_lineno"><code>end_lineno</code></a> are the first and last line numbers of source text span (1-indexed so the first line is line 1) and the <a class="reference internal" href="#ast.AST.col_offset" title="ast.AST.col_offset"><code>col_offset</code></a> and <a class="reference internal" href="#ast.AST.end_col_offset" title="ast.AST.end_col_offset"><code>end_col_offset</code></a> are the corresponding UTF-8 byte offsets of the first and last tokens that generated the node. The UTF-8 offset is recorded because the parser uses UTF-8 internally.</p> <p>Note that the end positions are not required by the compiler and are therefore optional. The end offset is <em>after</em> the last symbol, for example one can get the source segment of a one-line expression node using <code>source_line[node.col_offset : node.end_col_offset]</code>.</p> </dd>
</dl> <p>The constructor of a class <code>ast.T</code> parses its arguments as follows:</p> <ul class="simple"> <li>If there are positional arguments, there must be as many as there are items in <code>T._fields</code>; they will be assigned as attributes of these names.</li> <li>If there are keyword arguments, they will set the attributes of the same names to the given values.</li> </ul> <p>For example, to create and populate an <a class="reference internal" href="#ast.UnaryOp" title="ast.UnaryOp"><code>ast.UnaryOp</code></a> node, you could use</p> <pre data-language="python">node = ast.UnaryOp()
node.op = ast.USub()
node.operand = ast.Constant()
node.operand.value = 5
node.operand.lineno = 0
node.operand.col_offset = 0
node.lineno = 0
node.col_offset = 0
</pre> <p>or the more compact</p> <pre data-language="python">node = ast.UnaryOp(ast.USub(), ast.Constant(5, lineno=0, col_offset=0),
                   lineno=0, col_offset=0)
</pre> </dd>
</dl> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.8: </span>Class <a class="reference internal" href="#ast.Constant" title="ast.Constant"><code>ast.Constant</code></a> is now used for all constants.</p> </div> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.9: </span>Simple indices are represented by their value, extended slices are represented as tuples.</p> </div> <div class="deprecated"> <p><span class="versionmodified deprecated">Deprecated since version 3.8: </span>Old classes <code>ast.Num</code>, <code>ast.Str</code>, <code>ast.Bytes</code>, <code>ast.NameConstant</code> and <code>ast.Ellipsis</code> are still available, but they will be removed in future Python releases. In the meantime, instantiating them will return an instance of a different class.</p> </div> <div class="deprecated"> <p><span class="versionmodified deprecated">Deprecated since version 3.9: </span>Old classes <code>ast.Index</code> and <code>ast.ExtSlice</code> are still available, but they will be removed in future Python releases. In the meantime, instantiating them will return an instance of a different class.</p> </div> <div class="admonition note"> <p class="admonition-title">Note</p> <p>The descriptions of the specific node classes displayed here were initially adapted from the fantastic <a class="reference external" href="https://greentreesnakes.readthedocs.io/en/latest/">Green Tree Snakes</a> project and all its contributors.</p> </div> <section id="root-nodes"> <span id="ast-root-nodes"></span><h3>Root nodes</h3> <dl class="py class"> <dt class="sig sig-object py" id="ast.Module">
<code>class ast.Module(body, type_ignores)</code> </dt> <dd>
<p>A Python module, as with <a class="reference internal" href="../reference/toplevel_components#file-input"><span class="std std-ref">file input</span></a>. Node type generated by <a class="reference internal" href="#ast.parse" title="ast.parse"><code>ast.parse()</code></a> in the default <code>"exec"</code> <em>mode</em>.</p> <p><em>body</em> is a <a class="reference internal" href="stdtypes#list" title="list"><code>list</code></a> of the module’s <a class="reference internal" href="#ast-statements"><span class="std std-ref">Statements</span></a>.</p> <p><em>type_ignores</em> is a <a class="reference internal" href="stdtypes#list" title="list"><code>list</code></a> of the module’s type ignore comments; see <a class="reference internal" href="#ast.parse" title="ast.parse"><code>ast.parse()</code></a> for more details.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('x = 1'), indent=4))
Module(
    body=[
        Assign(
            targets=[
                Name(id='x', ctx=Store())],
            value=Constant(value=1))],
    type_ignores=[])
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.Expression">
<code>class ast.Expression(body)</code> </dt> <dd>
<p>A single Python <a class="reference internal" href="../reference/toplevel_components#expression-input"><span class="std std-ref">expression input</span></a>. Node type generated by <a class="reference internal" href="#ast.parse" title="ast.parse"><code>ast.parse()</code></a> when <em>mode</em> is <code>"eval"</code>.</p> <p><em>body</em> is a single node, one of the <a class="reference internal" href="#ast-expressions"><span class="std std-ref">expression types</span></a>.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('123', mode='eval'), indent=4))
Expression(
    body=Constant(value=123))
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.Interactive">
<code>class ast.Interactive(body)</code> </dt> <dd>
<p>A single <a class="reference internal" href="../reference/toplevel_components#interactive"><span class="std std-ref">interactive input</span></a>, like in <a class="reference internal" href="../tutorial/appendix#tut-interac"><span class="std std-ref">Interactive Mode</span></a>. Node type generated by <a class="reference internal" href="#ast.parse" title="ast.parse"><code>ast.parse()</code></a> when <em>mode</em> is <code>"single"</code>.</p> <p><em>body</em> is a <a class="reference internal" href="stdtypes#list" title="list"><code>list</code></a> of <a class="reference internal" href="#ast-statements"><span class="std std-ref">statement nodes</span></a>.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('x = 1; y = 2', mode='single'), indent=4))
Interactive(
    body=[
        Assign(
            targets=[
                Name(id='x', ctx=Store())],
            value=Constant(value=1)),
        Assign(
            targets=[
                Name(id='y', ctx=Store())],
            value=Constant(value=2))])
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.FunctionType">
<code>class ast.FunctionType(argtypes, returns)</code> </dt> <dd>
<p>A representation of an old-style type comments for functions, as Python versions prior to 3.5 didn’t support <span class="target" id="index-2"></span><a class="pep reference external" href="https://peps.python.org/pep-0484/"><strong>PEP 484</strong></a> annotations. Node type generated by <a class="reference internal" href="#ast.parse" title="ast.parse"><code>ast.parse()</code></a> when <em>mode</em> is <code>"func_type"</code>.</p> <p>Such type comments would look like this:</p> <pre data-language="python">def sum_two_number(a, b):
    # type: (int, int) -&gt; int
    return a + b
</pre> <p><em>argtypes</em> is a <a class="reference internal" href="stdtypes#list" title="list"><code>list</code></a> of <a class="reference internal" href="#ast-expressions"><span class="std std-ref">expression nodes</span></a>.</p> <p><em>returns</em> is a single <a class="reference internal" href="#ast-expressions"><span class="std std-ref">expression node</span></a>.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('(int, str) -&gt; List[int]', mode='func_type'), indent=4))
FunctionType(
    argtypes=[
        Name(id='int', ctx=Load()),
        Name(id='str', ctx=Load())],
    returns=Subscript(
        value=Name(id='List', ctx=Load()),
        slice=Name(id='int', ctx=Load()),
        ctx=Load()))
</pre> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.8.</span></p> </div> </dd>
</dl> </section> <section id="literals"> <h3>Literals</h3> <dl class="py class"> <dt class="sig sig-object py" id="ast.Constant">
<code>class ast.Constant(value)</code> </dt> <dd>
<p>A constant value. The <code>value</code> attribute of the <code>Constant</code> literal contains the Python object it represents. The values represented can be simple types such as a number, string or <code>None</code>, but also immutable container types (tuples and frozensets) if all of their elements are constant.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('123', mode='eval'), indent=4))
Expression(
    body=Constant(value=123))
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.FormattedValue">
<code>class ast.FormattedValue(value, conversion, format_spec)</code> </dt> <dd>
<p>Node representing a single formatting field in an f-string. If the string contains a single formatting field and nothing else the node can be isolated otherwise it appears in <a class="reference internal" href="#ast.JoinedStr" title="ast.JoinedStr"><code>JoinedStr</code></a>.</p> <ul class="simple"> <li>
<code>value</code> is any expression node (such as a literal, a variable, or a function call).</li> <li>
<p><code>conversion</code> is an integer:</p> <ul> <li>-1: no formatting</li> <li>115: <code>!s</code> string formatting</li> <li>114: <code>!r</code> repr formatting</li> <li>97: <code>!a</code> ascii formatting</li> </ul> </li> <li>
<code>format_spec</code> is a <a class="reference internal" href="#ast.JoinedStr" title="ast.JoinedStr"><code>JoinedStr</code></a> node representing the formatting of the value, or <code>None</code> if no format was specified. Both <code>conversion</code> and <code>format_spec</code> can be set at the same time.</li> </ul> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.JoinedStr">
<code>class ast.JoinedStr(values)</code> </dt> <dd>
<p>An f-string, comprising a series of <a class="reference internal" href="#ast.FormattedValue" title="ast.FormattedValue"><code>FormattedValue</code></a> and <a class="reference internal" href="#ast.Constant" title="ast.Constant"><code>Constant</code></a> nodes.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('f"sin({a}) is {sin(a):.3}"', mode='eval'), indent=4))
Expression(
    body=JoinedStr(
        values=[
            Constant(value='sin('),
            FormattedValue(
                value=Name(id='a', ctx=Load()),
                conversion=-1),
            Constant(value=') is '),
            FormattedValue(
                value=Call(
                    func=Name(id='sin', ctx=Load()),
                    args=[
                        Name(id='a', ctx=Load())],
                    keywords=[]),
                conversion=-1,
                format_spec=JoinedStr(
                    values=[
                        Constant(value='.3')]))]))
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.List">
<code>class ast.List(elts, ctx)</code> </dt> <dt class="sig sig-object py" id="ast.Tuple">
<code>class ast.Tuple(elts, ctx)</code> </dt> <dd>
<p>A list or tuple. <code>elts</code> holds a list of nodes representing the elements. <code>ctx</code> is <a class="reference internal" href="#ast.Store" title="ast.Store"><code>Store</code></a> if the container is an assignment target (i.e. <code>(x,y)=something</code>), and <a class="reference internal" href="#ast.Load" title="ast.Load"><code>Load</code></a> otherwise.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('[1, 2, 3]', mode='eval'), indent=4))
Expression(
    body=List(
        elts=[
            Constant(value=1),
            Constant(value=2),
            Constant(value=3)],
        ctx=Load()))
&gt;&gt;&gt; print(ast.dump(ast.parse('(1, 2, 3)', mode='eval'), indent=4))
Expression(
    body=Tuple(
        elts=[
            Constant(value=1),
            Constant(value=2),
            Constant(value=3)],
        ctx=Load()))
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.Set">
<code>class ast.Set(elts)</code> </dt> <dd>
<p>A set. <code>elts</code> holds a list of nodes representing the set’s elements.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('{1, 2, 3}', mode='eval'), indent=4))
Expression(
    body=Set(
        elts=[
            Constant(value=1),
            Constant(value=2),
            Constant(value=3)]))
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.Dict">
<code>class ast.Dict(keys, values)</code> </dt> <dd>
<p>A dictionary. <code>keys</code> and <code>values</code> hold lists of nodes representing the keys and the values respectively, in matching order (what would be returned when calling <code>dictionary.keys()</code> and <code>dictionary.values()</code>).</p> <p>When doing dictionary unpacking using dictionary literals the expression to be expanded goes in the <code>values</code> list, with a <code>None</code> at the corresponding position in <code>keys</code>.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('{"a":1, **d}', mode='eval'), indent=4))
Expression(
    body=Dict(
        keys=[
            Constant(value='a'),
            None],
        values=[
            Constant(value=1),
            Name(id='d', ctx=Load())]))
</pre> </dd>
</dl> </section> <section id="variables"> <h3>Variables</h3> <dl class="py class"> <dt class="sig sig-object py" id="ast.Name">
<code>class ast.Name(id, ctx)</code> </dt> <dd>
<p>A variable name. <code>id</code> holds the name as a string, and <code>ctx</code> is one of the following types.</p> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.Load">
<code>class ast.Load</code> </dt> <dt class="sig sig-object py" id="ast.Store">
<code>class ast.Store</code> </dt> <dt class="sig sig-object py" id="ast.Del">
<code>class ast.Del</code> </dt> <dd>
<p>Variable references can be used to load the value of a variable, to assign a new value to it, or to delete it. Variable references are given a context to distinguish these cases.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('a'), indent=4))
Module(
    body=[
        Expr(
            value=Name(id='a', ctx=Load()))],
    type_ignores=[])

&gt;&gt;&gt; print(ast.dump(ast.parse('a = 1'), indent=4))
Module(
    body=[
        Assign(
            targets=[
                Name(id='a', ctx=Store())],
            value=Constant(value=1))],
    type_ignores=[])

&gt;&gt;&gt; print(ast.dump(ast.parse('del a'), indent=4))
Module(
    body=[
        Delete(
            targets=[
                Name(id='a', ctx=Del())])],
    type_ignores=[])
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.Starred">
<code>class ast.Starred(value, ctx)</code> </dt> <dd>
<p>A <code>*var</code> variable reference. <code>value</code> holds the variable, typically a <a class="reference internal" href="#ast.Name" title="ast.Name"><code>Name</code></a> node. This type must be used when building a <a class="reference internal" href="#ast.Call" title="ast.Call"><code>Call</code></a> node with <code>*args</code>.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('a, *b = it'), indent=4))
Module(
    body=[
        Assign(
            targets=[
                Tuple(
                    elts=[
                        Name(id='a', ctx=Store()),
                        Starred(
                            value=Name(id='b', ctx=Store()),
                            ctx=Store())],
                    ctx=Store())],
            value=Name(id='it', ctx=Load()))],
    type_ignores=[])
</pre> </dd>
</dl> </section> <section id="expressions"> <span id="ast-expressions"></span><h3>Expressions</h3> <dl class="py class"> <dt class="sig sig-object py" id="ast.Expr">
<code>class ast.Expr(value)</code> </dt> <dd>
<p>When an expression, such as a function call, appears as a statement by itself with its return value not used or stored, it is wrapped in this container. <code>value</code> holds one of the other nodes in this section, a <a class="reference internal" href="#ast.Constant" title="ast.Constant"><code>Constant</code></a>, a <a class="reference internal" href="#ast.Name" title="ast.Name"><code>Name</code></a>, a <a class="reference internal" href="#ast.Lambda" title="ast.Lambda"><code>Lambda</code></a>, a <a class="reference internal" href="#ast.Yield" title="ast.Yield"><code>Yield</code></a> or <a class="reference internal" href="#ast.YieldFrom" title="ast.YieldFrom"><code>YieldFrom</code></a> node.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('-a'), indent=4))
Module(
    body=[
        Expr(
            value=UnaryOp(
                op=USub(),
                operand=Name(id='a', ctx=Load())))],
    type_ignores=[])
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.UnaryOp">
<code>class ast.UnaryOp(op, operand)</code> </dt> <dd>
<p>A unary operation. <code>op</code> is the operator, and <code>operand</code> any expression node.</p> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.UAdd">
<code>class ast.UAdd</code> </dt> <dt class="sig sig-object py" id="ast.USub">
<code>class ast.USub</code> </dt> <dt class="sig sig-object py" id="ast.Not">
<code>class ast.Not</code> </dt> <dt class="sig sig-object py" id="ast.Invert">
<code>class ast.Invert</code> </dt> <dd>
<p>Unary operator tokens. <a class="reference internal" href="#ast.Not" title="ast.Not"><code>Not</code></a> is the <code>not</code> keyword, <a class="reference internal" href="#ast.Invert" title="ast.Invert"><code>Invert</code></a> is the <code>~</code> operator.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('not x', mode='eval'), indent=4))
Expression(
    body=UnaryOp(
        op=Not(),
        operand=Name(id='x', ctx=Load())))
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.BinOp">
<code>class ast.BinOp(left, op, right)</code> </dt> <dd>
<p>A binary operation (like addition or division). <code>op</code> is the operator, and <code>left</code> and <code>right</code> are any expression nodes.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('x + y', mode='eval'), indent=4))
Expression(
    body=BinOp(
        left=Name(id='x', ctx=Load()),
        op=Add(),
        right=Name(id='y', ctx=Load())))
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.Add">
<code>class ast.Add</code> </dt> <dt class="sig sig-object py" id="ast.Sub">
<code>class ast.Sub</code> </dt> <dt class="sig sig-object py" id="ast.Mult">
<code>class ast.Mult</code> </dt> <dt class="sig sig-object py" id="ast.Div">
<code>class ast.Div</code> </dt> <dt class="sig sig-object py" id="ast.FloorDiv">
<code>class ast.FloorDiv</code> </dt> <dt class="sig sig-object py" id="ast.Mod">
<code>class ast.Mod</code> </dt> <dt class="sig sig-object py" id="ast.Pow">
<code>class ast.Pow</code> </dt> <dt class="sig sig-object py" id="ast.LShift">
<code>class ast.LShift</code> </dt> <dt class="sig sig-object py" id="ast.RShift">
<code>class ast.RShift</code> </dt> <dt class="sig sig-object py" id="ast.BitOr">
<code>class ast.BitOr</code> </dt> <dt class="sig sig-object py" id="ast.BitXor">
<code>class ast.BitXor</code> </dt> <dt class="sig sig-object py" id="ast.BitAnd">
<code>class ast.BitAnd</code> </dt> <dt class="sig sig-object py" id="ast.MatMult">
<code>class ast.MatMult</code> </dt> <dd>
<p>Binary operator tokens.</p> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.BoolOp">
<code>class ast.BoolOp(op, values)</code> </dt> <dd>
<p>A boolean operation, ‘or’ or ‘and’. <code>op</code> is <a class="reference internal" href="#ast.Or" title="ast.Or"><code>Or</code></a> or <a class="reference internal" href="#ast.And" title="ast.And"><code>And</code></a>. <code>values</code> are the values involved. Consecutive operations with the same operator, such as <code>a or b or c</code>, are collapsed into one node with several values.</p> <p>This doesn’t include <code>not</code>, which is a <a class="reference internal" href="#ast.UnaryOp" title="ast.UnaryOp"><code>UnaryOp</code></a>.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('x or y', mode='eval'), indent=4))
Expression(
    body=BoolOp(
        op=Or(),
        values=[
            Name(id='x', ctx=Load()),
            Name(id='y', ctx=Load())]))
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.And">
<code>class ast.And</code> </dt> <dt class="sig sig-object py" id="ast.Or">
<code>class ast.Or</code> </dt> <dd>
<p>Boolean operator tokens.</p> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.Compare">
<code>class ast.Compare(left, ops, comparators)</code> </dt> <dd>
<p>A comparison of two or more values. <code>left</code> is the first value in the comparison, <code>ops</code> the list of operators, and <code>comparators</code> the list of values after the first element in the comparison.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('1 &lt;= a &lt; 10', mode='eval'), indent=4))
Expression(
    body=Compare(
        left=Constant(value=1),
        ops=[
            LtE(),
            Lt()],
        comparators=[
            Name(id='a', ctx=Load()),
            Constant(value=10)]))
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.Eq">
<code>class ast.Eq</code> </dt> <dt class="sig sig-object py" id="ast.NotEq">
<code>class ast.NotEq</code> </dt> <dt class="sig sig-object py" id="ast.Lt">
<code>class ast.Lt</code> </dt> <dt class="sig sig-object py" id="ast.LtE">
<code>class ast.LtE</code> </dt> <dt class="sig sig-object py" id="ast.Gt">
<code>class ast.Gt</code> </dt> <dt class="sig sig-object py" id="ast.GtE">
<code>class ast.GtE</code> </dt> <dt class="sig sig-object py" id="ast.Is">
<code>class ast.Is</code> </dt> <dt class="sig sig-object py" id="ast.IsNot">
<code>class ast.IsNot</code> </dt> <dt class="sig sig-object py" id="ast.In">
<code>class ast.In</code> </dt> <dt class="sig sig-object py" id="ast.NotIn">
<code>class ast.NotIn</code> </dt> <dd>
<p>Comparison operator tokens.</p> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.Call">
<code>class ast.Call(func, args, keywords)</code> </dt> <dd>
<p>A function call. <code>func</code> is the function, which will often be a <a class="reference internal" href="#ast.Name" title="ast.Name"><code>Name</code></a> or <a class="reference internal" href="#ast.Attribute" title="ast.Attribute"><code>Attribute</code></a> object. Of the arguments:</p> <ul class="simple"> <li>
<code>args</code> holds a list of the arguments passed by position.</li> <li>
<code>keywords</code> holds a list of <a class="reference internal" href="#ast.keyword" title="ast.keyword"><code>keyword</code></a> objects representing arguments passed by keyword.</li> </ul> <p>When creating a <code>Call</code> node, <code>args</code> and <code>keywords</code> are required, but they can be empty lists.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('func(a, b=c, *d, **e)', mode='eval'), indent=4))
Expression(
    body=Call(
        func=Name(id='func', ctx=Load()),
        args=[
            Name(id='a', ctx=Load()),
            Starred(
                value=Name(id='d', ctx=Load()),
                ctx=Load())],
        keywords=[
            keyword(
                arg='b',
                value=Name(id='c', ctx=Load())),
            keyword(
                value=Name(id='e', ctx=Load()))]))
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.keyword">
<code>class ast.keyword(arg, value)</code> </dt> <dd>
<p>A keyword argument to a function call or class definition. <code>arg</code> is a raw string of the parameter name, <code>value</code> is a node to pass in.</p> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.IfExp">
<code>class ast.IfExp(test, body, orelse)</code> </dt> <dd>
<p>An expression such as <code>a if b else c</code>. Each field holds a single node, so in the following example, all three are <a class="reference internal" href="#ast.Name" title="ast.Name"><code>Name</code></a> nodes.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('a if b else c', mode='eval'), indent=4))
Expression(
    body=IfExp(
        test=Name(id='b', ctx=Load()),
        body=Name(id='a', ctx=Load()),
        orelse=Name(id='c', ctx=Load())))
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.Attribute">
<code>class ast.Attribute(value, attr, ctx)</code> </dt> <dd>
<p>Attribute access, e.g. <code>d.keys</code>. <code>value</code> is a node, typically a <a class="reference internal" href="#ast.Name" title="ast.Name"><code>Name</code></a>. <code>attr</code> is a bare string giving the name of the attribute, and <code>ctx</code> is <a class="reference internal" href="#ast.Load" title="ast.Load"><code>Load</code></a>, <a class="reference internal" href="#ast.Store" title="ast.Store"><code>Store</code></a> or <a class="reference internal" href="#ast.Del" title="ast.Del"><code>Del</code></a> according to how the attribute is acted on.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('snake.colour', mode='eval'), indent=4))
Expression(
    body=Attribute(
        value=Name(id='snake', ctx=Load()),
        attr='colour',
        ctx=Load()))
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.NamedExpr">
<code>class ast.NamedExpr(target, value)</code> </dt> <dd>
<p>A named expression. This AST node is produced by the assignment expressions operator (also known as the walrus operator). As opposed to the <a class="reference internal" href="#ast.Assign" title="ast.Assign"><code>Assign</code></a> node in which the first argument can be multiple nodes, in this case both <code>target</code> and <code>value</code> must be single nodes.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('(x := 4)', mode='eval'), indent=4))
Expression(
    body=NamedExpr(
        target=Name(id='x', ctx=Store()),
        value=Constant(value=4)))
</pre> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.8.</span></p> </div> </dd>
</dl> <section id="subscripting"> <h4>Subscripting</h4> <dl class="py class"> <dt class="sig sig-object py" id="ast.Subscript">
<code>class ast.Subscript(value, slice, ctx)</code> </dt> <dd>
<p>A subscript, such as <code>l[1]</code>. <code>value</code> is the subscripted object (usually sequence or mapping). <code>slice</code> is an index, slice or key. It can be a <a class="reference internal" href="#ast.Tuple" title="ast.Tuple"><code>Tuple</code></a> and contain a <a class="reference internal" href="#ast.Slice" title="ast.Slice"><code>Slice</code></a>. <code>ctx</code> is <a class="reference internal" href="#ast.Load" title="ast.Load"><code>Load</code></a>, <a class="reference internal" href="#ast.Store" title="ast.Store"><code>Store</code></a> or <a class="reference internal" href="#ast.Del" title="ast.Del"><code>Del</code></a> according to the action performed with the subscript.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('l[1:2, 3]', mode='eval'), indent=4))
Expression(
    body=Subscript(
        value=Name(id='l', ctx=Load()),
        slice=Tuple(
            elts=[
                Slice(
                    lower=Constant(value=1),
                    upper=Constant(value=2)),
                Constant(value=3)],
            ctx=Load()),
        ctx=Load()))
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.Slice">
<code>class ast.Slice(lower, upper, step)</code> </dt> <dd>
<p>Regular slicing (on the form <code>lower:upper</code> or <code>lower:upper:step</code>). Can occur only inside the <em>slice</em> field of <a class="reference internal" href="#ast.Subscript" title="ast.Subscript"><code>Subscript</code></a>, either directly or as an element of <a class="reference internal" href="#ast.Tuple" title="ast.Tuple"><code>Tuple</code></a>.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('l[1:2]', mode='eval'), indent=4))
Expression(
    body=Subscript(
        value=Name(id='l', ctx=Load()),
        slice=Slice(
            lower=Constant(value=1),
            upper=Constant(value=2)),
        ctx=Load()))
</pre> </dd>
</dl> </section> <section id="comprehensions"> <h4>Comprehensions</h4> <dl class="py class"> <dt class="sig sig-object py" id="ast.ListComp">
<code>class ast.ListComp(elt, generators)</code> </dt> <dt class="sig sig-object py" id="ast.SetComp">
<code>class ast.SetComp(elt, generators)</code> </dt> <dt class="sig sig-object py" id="ast.GeneratorExp">
<code>class ast.GeneratorExp(elt, generators)</code> </dt> <dt class="sig sig-object py" id="ast.DictComp">
<code>class ast.DictComp(key, value, generators)</code> </dt> <dd>
<p>List and set comprehensions, generator expressions, and dictionary comprehensions. <code>elt</code> (or <code>key</code> and <code>value</code>) is a single node representing the part that will be evaluated for each item.</p> <p><code>generators</code> is a list of <a class="reference internal" href="#ast.comprehension" title="ast.comprehension"><code>comprehension</code></a> nodes.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('[x for x in numbers]', mode='eval'), indent=4))
Expression(
    body=ListComp(
        elt=Name(id='x', ctx=Load()),
        generators=[
            comprehension(
                target=Name(id='x', ctx=Store()),
                iter=Name(id='numbers', ctx=Load()),
                ifs=[],
                is_async=0)]))
&gt;&gt;&gt; print(ast.dump(ast.parse('{x: x**2 for x in numbers}', mode='eval'), indent=4))
Expression(
    body=DictComp(
        key=Name(id='x', ctx=Load()),
        value=BinOp(
            left=Name(id='x', ctx=Load()),
            op=Pow(),
            right=Constant(value=2)),
        generators=[
            comprehension(
                target=Name(id='x', ctx=Store()),
                iter=Name(id='numbers', ctx=Load()),
                ifs=[],
                is_async=0)]))
&gt;&gt;&gt; print(ast.dump(ast.parse('{x for x in numbers}', mode='eval'), indent=4))
Expression(
    body=SetComp(
        elt=Name(id='x', ctx=Load()),
        generators=[
            comprehension(
                target=Name(id='x', ctx=Store()),
                iter=Name(id='numbers', ctx=Load()),
                ifs=[],
                is_async=0)]))
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.comprehension">
<code>class ast.comprehension(target, iter, ifs, is_async)</code> </dt> <dd>
<p>One <code>for</code> clause in a comprehension. <code>target</code> is the reference to use for each element - typically a <a class="reference internal" href="#ast.Name" title="ast.Name"><code>Name</code></a> or <a class="reference internal" href="#ast.Tuple" title="ast.Tuple"><code>Tuple</code></a> node. <code>iter</code> is the object to iterate over. <code>ifs</code> is a list of test expressions: each <code>for</code> clause can have multiple <code>ifs</code>.</p> <p><code>is_async</code> indicates a comprehension is asynchronous (using an <code>async for</code> instead of <code>for</code>). The value is an integer (0 or 1).</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('[ord(c) for line in file for c in line]', mode='eval'),
...                indent=4)) # Multiple comprehensions in one.
Expression(
    body=ListComp(
        elt=Call(
            func=Name(id='ord', ctx=Load()),
            args=[
                Name(id='c', ctx=Load())],
            keywords=[]),
        generators=[
            comprehension(
                target=Name(id='line', ctx=Store()),
                iter=Name(id='file', ctx=Load()),
                ifs=[],
                is_async=0),
            comprehension(
                target=Name(id='c', ctx=Store()),
                iter=Name(id='line', ctx=Load()),
                ifs=[],
                is_async=0)]))

&gt;&gt;&gt; print(ast.dump(ast.parse('(n**2 for n in it if n&gt;5 if n&lt;10)', mode='eval'),
...                indent=4)) # generator comprehension
Expression(
    body=GeneratorExp(
        elt=BinOp(
            left=Name(id='n', ctx=Load()),
            op=Pow(),
            right=Constant(value=2)),
        generators=[
            comprehension(
                target=Name(id='n', ctx=Store()),
                iter=Name(id='it', ctx=Load()),
                ifs=[
                    Compare(
                        left=Name(id='n', ctx=Load()),
                        ops=[
                            Gt()],
                        comparators=[
                            Constant(value=5)]),
                    Compare(
                        left=Name(id='n', ctx=Load()),
                        ops=[
                            Lt()],
                        comparators=[
                            Constant(value=10)])],
                is_async=0)]))

&gt;&gt;&gt; print(ast.dump(ast.parse('[i async for i in soc]', mode='eval'),
...                indent=4)) # Async comprehension
Expression(
    body=ListComp(
        elt=Name(id='i', ctx=Load()),
        generators=[
            comprehension(
                target=Name(id='i', ctx=Store()),
                iter=Name(id='soc', ctx=Load()),
                ifs=[],
                is_async=1)]))
</pre> </dd>
</dl> </section> </section> <section id="statements"> <span id="ast-statements"></span><h3>Statements</h3> <dl class="py class"> <dt class="sig sig-object py" id="ast.Assign">
<code>class ast.Assign(targets, value, type_comment)</code> </dt> <dd>
<p>An assignment. <code>targets</code> is a list of nodes, and <code>value</code> is a single node.</p> <p>Multiple nodes in <code>targets</code> represents assigning the same value to each. Unpacking is represented by putting a <a class="reference internal" href="#ast.Tuple" title="ast.Tuple"><code>Tuple</code></a> or <a class="reference internal" href="#ast.List" title="ast.List"><code>List</code></a> within <code>targets</code>.</p> <dl class="py attribute"> <dt class="sig sig-object py" id="ast.Assign.type_comment">
<code>type_comment</code> </dt> <dd>
<p><code>type_comment</code> is an optional string with the type annotation as a comment.</p> </dd>
</dl> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('a = b = 1'), indent=4)) # Multiple assignment
Module(
    body=[
        Assign(
            targets=[
                Name(id='a', ctx=Store()),
                Name(id='b', ctx=Store())],
            value=Constant(value=1))],
    type_ignores=[])

&gt;&gt;&gt; print(ast.dump(ast.parse('a,b = c'), indent=4)) # Unpacking
Module(
    body=[
        Assign(
            targets=[
                Tuple(
                    elts=[
                        Name(id='a', ctx=Store()),
                        Name(id='b', ctx=Store())],
                    ctx=Store())],
            value=Name(id='c', ctx=Load()))],
    type_ignores=[])
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.AnnAssign">
<code>class ast.AnnAssign(target, annotation, value, simple)</code> </dt> <dd>
<p>An assignment with a type annotation. <code>target</code> is a single node and can be a <a class="reference internal" href="#ast.Name" title="ast.Name"><code>Name</code></a>, a <a class="reference internal" href="#ast.Attribute" title="ast.Attribute"><code>Attribute</code></a> or a <a class="reference internal" href="#ast.Subscript" title="ast.Subscript"><code>Subscript</code></a>. <code>annotation</code> is the annotation, such as a <a class="reference internal" href="#ast.Constant" title="ast.Constant"><code>Constant</code></a> or <a class="reference internal" href="#ast.Name" title="ast.Name"><code>Name</code></a> node. <code>value</code> is a single optional node. <code>simple</code> is a boolean integer set to True for a <a class="reference internal" href="#ast.Name" title="ast.Name"><code>Name</code></a> node in <code>target</code> that do not appear in between parenthesis and are hence pure names and not expressions.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('c: int'), indent=4))
Module(
    body=[
        AnnAssign(
            target=Name(id='c', ctx=Store()),
            annotation=Name(id='int', ctx=Load()),
            simple=1)],
    type_ignores=[])

&gt;&gt;&gt; print(ast.dump(ast.parse('(a): int = 1'), indent=4)) # Annotation with parenthesis
Module(
    body=[
        AnnAssign(
            target=Name(id='a', ctx=Store()),
            annotation=Name(id='int', ctx=Load()),
            value=Constant(value=1),
            simple=0)],
    type_ignores=[])

&gt;&gt;&gt; print(ast.dump(ast.parse('a.b: int'), indent=4)) # Attribute annotation
Module(
    body=[
        AnnAssign(
            target=Attribute(
                value=Name(id='a', ctx=Load()),
                attr='b',
                ctx=Store()),
            annotation=Name(id='int', ctx=Load()),
            simple=0)],
    type_ignores=[])

&gt;&gt;&gt; print(ast.dump(ast.parse('a[1]: int'), indent=4)) # Subscript annotation
Module(
    body=[
        AnnAssign(
            target=Subscript(
                value=Name(id='a', ctx=Load()),
                slice=Constant(value=1),
                ctx=Store()),
            annotation=Name(id='int', ctx=Load()),
            simple=0)],
    type_ignores=[])
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.AugAssign">
<code>class ast.AugAssign(target, op, value)</code> </dt> <dd>
<p>Augmented assignment, such as <code>a += 1</code>. In the following example, <code>target</code> is a <a class="reference internal" href="#ast.Name" title="ast.Name"><code>Name</code></a> node for <code>x</code> (with the <a class="reference internal" href="#ast.Store" title="ast.Store"><code>Store</code></a> context), <code>op</code> is <a class="reference internal" href="#ast.Add" title="ast.Add"><code>Add</code></a>, and <code>value</code> is a <a class="reference internal" href="#ast.Constant" title="ast.Constant"><code>Constant</code></a> with value for 1.</p> <p>The <code>target</code> attribute cannot be of class <a class="reference internal" href="#ast.Tuple" title="ast.Tuple"><code>Tuple</code></a> or <a class="reference internal" href="#ast.List" title="ast.List"><code>List</code></a>, unlike the targets of <a class="reference internal" href="#ast.Assign" title="ast.Assign"><code>Assign</code></a>.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('x += 2'), indent=4))
Module(
    body=[
        AugAssign(
            target=Name(id='x', ctx=Store()),
            op=Add(),
            value=Constant(value=2))],
    type_ignores=[])
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.Raise">
<code>class ast.Raise(exc, cause)</code> </dt> <dd>
<p>A <code>raise</code> statement. <code>exc</code> is the exception object to be raised, normally a <a class="reference internal" href="#ast.Call" title="ast.Call"><code>Call</code></a> or <a class="reference internal" href="#ast.Name" title="ast.Name"><code>Name</code></a>, or <code>None</code> for a standalone <code>raise</code>. <code>cause</code> is the optional part for <code>y</code> in <code>raise x from y</code>.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('raise x from y'), indent=4))
Module(
    body=[
        Raise(
            exc=Name(id='x', ctx=Load()),
            cause=Name(id='y', ctx=Load()))],
    type_ignores=[])
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.Assert">
<code>class ast.Assert(test, msg)</code> </dt> <dd>
<p>An assertion. <code>test</code> holds the condition, such as a <a class="reference internal" href="#ast.Compare" title="ast.Compare"><code>Compare</code></a> node. <code>msg</code> holds the failure message.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('assert x,y'), indent=4))
Module(
    body=[
        Assert(
            test=Name(id='x', ctx=Load()),
            msg=Name(id='y', ctx=Load()))],
    type_ignores=[])
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.Delete">
<code>class ast.Delete(targets)</code> </dt> <dd>
<p>Represents a <code>del</code> statement. <code>targets</code> is a list of nodes, such as <a class="reference internal" href="#ast.Name" title="ast.Name"><code>Name</code></a>, <a class="reference internal" href="#ast.Attribute" title="ast.Attribute"><code>Attribute</code></a> or <a class="reference internal" href="#ast.Subscript" title="ast.Subscript"><code>Subscript</code></a> nodes.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('del x,y,z'), indent=4))
Module(
    body=[
        Delete(
            targets=[
                Name(id='x', ctx=Del()),
                Name(id='y', ctx=Del()),
                Name(id='z', ctx=Del())])],
    type_ignores=[])
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.Pass">
<code>class ast.Pass</code> </dt> <dd>
<p>A <code>pass</code> statement.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('pass'), indent=4))
Module(
    body=[
        Pass()],
    type_ignores=[])
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.TypeAlias">
<code>class ast.TypeAlias(name, type_params, value)</code> </dt> <dd>
<p>A <a class="reference internal" href="typing#type-aliases"><span class="std std-ref">type alias</span></a> created through the <a class="reference internal" href="../reference/simple_stmts#type"><code>type</code></a> statement. <code>name</code> is the name of the alias, <code>type_params</code> is a list of <a class="reference internal" href="#ast-type-params"><span class="std std-ref">type parameters</span></a>, and <code>value</code> is the value of the type alias.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('type Alias = int'), indent=4))
Module(
    body=[
        TypeAlias(
            name=Name(id='Alias', ctx=Store()),
            type_params=[],
            value=Name(id='int', ctx=Load()))],
    type_ignores=[])
</pre> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.12.</span></p> </div> </dd>
</dl> <p>Other statements which are only applicable inside functions or loops are described in other sections.</p> <section id="imports"> <h4>Imports</h4> <dl class="py class"> <dt class="sig sig-object py" id="ast.Import">
<code>class ast.Import(names)</code> </dt> <dd>
<p>An import statement. <code>names</code> is a list of <a class="reference internal" href="#ast.alias" title="ast.alias"><code>alias</code></a> nodes.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('import x,y,z'), indent=4))
Module(
    body=[
        Import(
            names=[
                alias(name='x'),
                alias(name='y'),
                alias(name='z')])],
    type_ignores=[])
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.ImportFrom">
<code>class ast.ImportFrom(module, names, level)</code> </dt> <dd>
<p>Represents <code>from x import y</code>. <code>module</code> is a raw string of the ‘from’ name, without any leading dots, or <code>None</code> for statements such as <code>from . import foo</code>. <code>level</code> is an integer holding the level of the relative import (0 means absolute import).</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('from y import x,y,z'), indent=4))
Module(
    body=[
        ImportFrom(
            module='y',
            names=[
                alias(name='x'),
                alias(name='y'),
                alias(name='z')],
            level=0)],
    type_ignores=[])
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.alias">
<code>class ast.alias(name, asname)</code> </dt> <dd>
<p>Both parameters are raw strings of the names. <code>asname</code> can be <code>None</code> if the regular name is to be used.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('from ..foo.bar import a as b, c'), indent=4))
Module(
    body=[
        ImportFrom(
            module='foo.bar',
            names=[
                alias(name='a', asname='b'),
                alias(name='c')],
            level=2)],
    type_ignores=[])
</pre> </dd>
</dl> </section> </section> <section id="control-flow"> <h3>Control flow</h3> <div class="admonition note"> <p class="admonition-title">Note</p> <p>Optional clauses such as <code>else</code> are stored as an empty list if they’re not present.</p> </div> <dl class="py class"> <dt class="sig sig-object py" id="ast.If">
<code>class ast.If(test, body, orelse)</code> </dt> <dd>
<p>An <code>if</code> statement. <code>test</code> holds a single node, such as a <a class="reference internal" href="#ast.Compare" title="ast.Compare"><code>Compare</code></a> node. <code>body</code> and <code>orelse</code> each hold a list of nodes.</p> <p><code>elif</code> clauses don’t have a special representation in the AST, but rather appear as extra <a class="reference internal" href="#ast.If" title="ast.If"><code>If</code></a> nodes within the <code>orelse</code> section of the previous one.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse("""
... if x:
...    ...
... elif y:
...    ...
... else:
...    ...
... """), indent=4))
Module(
    body=[
        If(
            test=Name(id='x', ctx=Load()),
            body=[
                Expr(
                    value=Constant(value=Ellipsis))],
            orelse=[
                If(
                    test=Name(id='y', ctx=Load()),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))],
                    orelse=[
                        Expr(
                            value=Constant(value=Ellipsis))])])],
    type_ignores=[])
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.For">
<code>class ast.For(target, iter, body, orelse, type_comment)</code> </dt> <dd>
<p>A <code>for</code> loop. <code>target</code> holds the variable(s) the loop assigns to, as a single <a class="reference internal" href="#ast.Name" title="ast.Name"><code>Name</code></a>, <a class="reference internal" href="#ast.Tuple" title="ast.Tuple"><code>Tuple</code></a>, <a class="reference internal" href="#ast.List" title="ast.List"><code>List</code></a>, <a class="reference internal" href="#ast.Attribute" title="ast.Attribute"><code>Attribute</code></a> or <a class="reference internal" href="#ast.Subscript" title="ast.Subscript"><code>Subscript</code></a> node. <code>iter</code> holds the item to be looped over, again as a single node. <code>body</code> and <code>orelse</code> contain lists of nodes to execute. Those in <code>orelse</code> are executed if the loop finishes normally, rather than via a <code>break</code> statement.</p> <dl class="py attribute"> <dt class="sig sig-object py" id="ast.For.type_comment">
<code>type_comment</code> </dt> <dd>
<p><code>type_comment</code> is an optional string with the type annotation as a comment.</p> </dd>
</dl> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse("""
... for x in y:
...     ...
... else:
...     ...
... """), indent=4))
Module(
    body=[
        For(
            target=Name(id='x', ctx=Store()),
            iter=Name(id='y', ctx=Load()),
            body=[
                Expr(
                    value=Constant(value=Ellipsis))],
            orelse=[
                Expr(
                    value=Constant(value=Ellipsis))])],
    type_ignores=[])
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.While">
<code>class ast.While(test, body, orelse)</code> </dt> <dd>
<p>A <code>while</code> loop. <code>test</code> holds the condition, such as a <a class="reference internal" href="#ast.Compare" title="ast.Compare"><code>Compare</code></a> node.</p> <pre data-language="pycon3">&gt;&gt; print(ast.dump(ast.parse("""
... while x:
...    ...
... else:
...    ...
... """), indent=4))
Module(
    body=[
        While(
            test=Name(id='x', ctx=Load()),
            body=[
                Expr(
                    value=Constant(value=Ellipsis))],
            orelse=[
                Expr(
                    value=Constant(value=Ellipsis))])],
    type_ignores=[])
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.Break">
<code>class ast.Break</code> </dt> <dt class="sig sig-object py" id="ast.Continue">
<code>class ast.Continue</code> </dt> <dd>
<p>The <code>break</code> and <code>continue</code> statements.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse("""\
... for a in b:
...     if a &gt; 5:
...         break
...     else:
...         continue
...
... """), indent=4))
Module(
    body=[
        For(
            target=Name(id='a', ctx=Store()),
            iter=Name(id='b', ctx=Load()),
            body=[
                If(
                    test=Compare(
                        left=Name(id='a', ctx=Load()),
                        ops=[
                            Gt()],
                        comparators=[
                            Constant(value=5)]),
                    body=[
                        Break()],
                    orelse=[
                        Continue()])],
            orelse=[])],
    type_ignores=[])
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.Try">
<code>class ast.Try(body, handlers, orelse, finalbody)</code> </dt> <dd>
<p><code>try</code> blocks. All attributes are list of nodes to execute, except for <code>handlers</code>, which is a list of <a class="reference internal" href="#ast.ExceptHandler" title="ast.ExceptHandler"><code>ExceptHandler</code></a> nodes.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse("""
... try:
...    ...
... except Exception:
...    ...
... except OtherException as e:
...    ...
... else:
...    ...
... finally:
...    ...
... """), indent=4))
Module(
    body=[
        Try(
            body=[
                Expr(
                    value=Constant(value=Ellipsis))],
            handlers=[
                ExceptHandler(
                    type=Name(id='Exception', ctx=Load()),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))]),
                ExceptHandler(
                    type=Name(id='OtherException', ctx=Load()),
                    name='e',
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))])],
            orelse=[
                Expr(
                    value=Constant(value=Ellipsis))],
            finalbody=[
                Expr(
                    value=Constant(value=Ellipsis))])],
    type_ignores=[])
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.TryStar">
<code>class ast.TryStar(body, handlers, orelse, finalbody)</code> </dt> <dd>
<p><code>try</code> blocks which are followed by <code>except*</code> clauses. The attributes are the same as for <a class="reference internal" href="#ast.Try" title="ast.Try"><code>Try</code></a> but the <a class="reference internal" href="#ast.ExceptHandler" title="ast.ExceptHandler"><code>ExceptHandler</code></a> nodes in <code>handlers</code> are interpreted as <code>except*</code> blocks rather then <code>except</code>.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse("""
... try:
...    ...
... except* Exception:
...    ...
... """), indent=4))
Module(
    body=[
        TryStar(
            body=[
                Expr(
                    value=Constant(value=Ellipsis))],
            handlers=[
                ExceptHandler(
                    type=Name(id='Exception', ctx=Load()),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))])],
            orelse=[],
            finalbody=[])],
    type_ignores=[])
</pre> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.11.</span></p> </div> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.ExceptHandler">
<code>class ast.ExceptHandler(type, name, body)</code> </dt> <dd>
<p>A single <code>except</code> clause. <code>type</code> is the exception type it will match, typically a <a class="reference internal" href="#ast.Name" title="ast.Name"><code>Name</code></a> node (or <code>None</code> for a catch-all <code>except:</code> clause). <code>name</code> is a raw string for the name to hold the exception, or <code>None</code> if the clause doesn’t have <code>as foo</code>. <code>body</code> is a list of nodes.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse("""\
... try:
...     a + 1
... except TypeError:
...     pass
... """), indent=4))
Module(
    body=[
        Try(
            body=[
                Expr(
                    value=BinOp(
                        left=Name(id='a', ctx=Load()),
                        op=Add(),
                        right=Constant(value=1)))],
            handlers=[
                ExceptHandler(
                    type=Name(id='TypeError', ctx=Load()),
                    body=[
                        Pass()])],
            orelse=[],
            finalbody=[])],
    type_ignores=[])
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.With">
<code>class ast.With(items, body, type_comment)</code> </dt> <dd>
<p>A <code>with</code> block. <code>items</code> is a list of <a class="reference internal" href="#ast.withitem" title="ast.withitem"><code>withitem</code></a> nodes representing the context managers, and <code>body</code> is the indented block inside the context.</p> <dl class="py attribute"> <dt class="sig sig-object py" id="ast.With.type_comment">
<code>type_comment</code> </dt> <dd>
<p><code>type_comment</code> is an optional string with the type annotation as a comment.</p> </dd>
</dl> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.withitem">
<code>class ast.withitem(context_expr, optional_vars)</code> </dt> <dd>
<p>A single context manager in a <code>with</code> block. <code>context_expr</code> is the context manager, often a <a class="reference internal" href="#ast.Call" title="ast.Call"><code>Call</code></a> node. <code>optional_vars</code> is a <a class="reference internal" href="#ast.Name" title="ast.Name"><code>Name</code></a>, <a class="reference internal" href="#ast.Tuple" title="ast.Tuple"><code>Tuple</code></a> or <a class="reference internal" href="#ast.List" title="ast.List"><code>List</code></a> for the <code>as foo</code> part, or <code>None</code> if that isn’t used.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse("""\
... with a as b, c as d:
...    something(b, d)
... """), indent=4))
Module(
    body=[
        With(
            items=[
                withitem(
                    context_expr=Name(id='a', ctx=Load()),
                    optional_vars=Name(id='b', ctx=Store())),
                withitem(
                    context_expr=Name(id='c', ctx=Load()),
                    optional_vars=Name(id='d', ctx=Store()))],
            body=[
                Expr(
                    value=Call(
                        func=Name(id='something', ctx=Load()),
                        args=[
                            Name(id='b', ctx=Load()),
                            Name(id='d', ctx=Load())],
                        keywords=[]))])],
    type_ignores=[])
</pre> </dd>
</dl> </section> <section id="pattern-matching"> <h3>Pattern matching</h3> <dl class="py class"> <dt class="sig sig-object py" id="ast.Match">
<code>class ast.Match(subject, cases)</code> </dt> <dd>
<p>A <code>match</code> statement. <code>subject</code> holds the subject of the match (the object that is being matched against the cases) and <code>cases</code> contains an iterable of <a class="reference internal" href="#ast.match_case" title="ast.match_case"><code>match_case</code></a> nodes with the different cases.</p> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.10.</span></p> </div> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.match_case">
<code>class ast.match_case(pattern, guard, body)</code> </dt> <dd>
<p>A single case pattern in a <code>match</code> statement. <code>pattern</code> contains the match pattern that the subject will be matched against. Note that the <a class="reference internal" href="#ast.AST" title="ast.AST"><code>AST</code></a> nodes produced for patterns differ from those produced for expressions, even when they share the same syntax.</p> <p>The <code>guard</code> attribute contains an expression that will be evaluated if the pattern matches the subject.</p> <p><code>body</code> contains a list of nodes to execute if the pattern matches and the result of evaluating the guard expression is true.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse("""
... match x:
...     case [x] if x&gt;0:
...         ...
...     case tuple():
...         ...
... """), indent=4))
Module(
    body=[
        Match(
            subject=Name(id='x', ctx=Load()),
            cases=[
                match_case(
                    pattern=MatchSequence(
                        patterns=[
                            MatchAs(name='x')]),
                    guard=Compare(
                        left=Name(id='x', ctx=Load()),
                        ops=[
                            Gt()],
                        comparators=[
                            Constant(value=0)]),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))]),
                match_case(
                    pattern=MatchClass(
                        cls=Name(id='tuple', ctx=Load()),
                        patterns=[],
                        kwd_attrs=[],
                        kwd_patterns=[]),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))])])],
    type_ignores=[])
</pre> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.10.</span></p> </div> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.MatchValue">
<code>class ast.MatchValue(value)</code> </dt> <dd>
<p>A match literal or value pattern that compares by equality. <code>value</code> is an expression node. Permitted value nodes are restricted as described in the match statement documentation. This pattern succeeds if the match subject is equal to the evaluated value.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse("""
... match x:
...     case "Relevant":
...         ...
... """), indent=4))
Module(
    body=[
        Match(
            subject=Name(id='x', ctx=Load()),
            cases=[
                match_case(
                    pattern=MatchValue(
                        value=Constant(value='Relevant')),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))])])],
    type_ignores=[])
</pre> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.10.</span></p> </div> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.MatchSingleton">
<code>class ast.MatchSingleton(value)</code> </dt> <dd>
<p>A match literal pattern that compares by identity. <code>value</code> is the singleton to be compared against: <code>None</code>, <code>True</code>, or <code>False</code>. This pattern succeeds if the match subject is the given constant.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse("""
... match x:
...     case None:
...         ...
... """), indent=4))
Module(
    body=[
        Match(
            subject=Name(id='x', ctx=Load()),
            cases=[
                match_case(
                    pattern=MatchSingleton(value=None),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))])])],
    type_ignores=[])
</pre> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.10.</span></p> </div> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.MatchSequence">
<code>class ast.MatchSequence(patterns)</code> </dt> <dd>
<p>A match sequence pattern. <code>patterns</code> contains the patterns to be matched against the subject elements if the subject is a sequence. Matches a variable length sequence if one of the subpatterns is a <code>MatchStar</code> node, otherwise matches a fixed length sequence.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse("""
... match x:
...     case [1, 2]:
...         ...
... """), indent=4))
Module(
    body=[
        Match(
            subject=Name(id='x', ctx=Load()),
            cases=[
                match_case(
                    pattern=MatchSequence(
                        patterns=[
                            MatchValue(
                                value=Constant(value=1)),
                            MatchValue(
                                value=Constant(value=2))]),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))])])],
    type_ignores=[])
</pre> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.10.</span></p> </div> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.MatchStar">
<code>class ast.MatchStar(name)</code> </dt> <dd>
<p>Matches the rest of the sequence in a variable length match sequence pattern. If <code>name</code> is not <code>None</code>, a list containing the remaining sequence elements is bound to that name if the overall sequence pattern is successful.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse("""
... match x:
...     case [1, 2, *rest]:
...         ...
...     case [*_]:
...         ...
... """), indent=4))
Module(
    body=[
        Match(
            subject=Name(id='x', ctx=Load()),
            cases=[
                match_case(
                    pattern=MatchSequence(
                        patterns=[
                            MatchValue(
                                value=Constant(value=1)),
                            MatchValue(
                                value=Constant(value=2)),
                            MatchStar(name='rest')]),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))]),
                match_case(
                    pattern=MatchSequence(
                        patterns=[
                            MatchStar()]),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))])])],
    type_ignores=[])
</pre> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.10.</span></p> </div> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.MatchMapping">
<code>class ast.MatchMapping(keys, patterns, rest)</code> </dt> <dd>
<p>A match mapping pattern. <code>keys</code> is a sequence of expression nodes. <code>patterns</code> is a corresponding sequence of pattern nodes. <code>rest</code> is an optional name that can be specified to capture the remaining mapping elements. Permitted key expressions are restricted as described in the match statement documentation.</p> <p>This pattern succeeds if the subject is a mapping, all evaluated key expressions are present in the mapping, and the value corresponding to each key matches the corresponding subpattern. If <code>rest</code> is not <code>None</code>, a dict containing the remaining mapping elements is bound to that name if the overall mapping pattern is successful.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse("""
... match x:
...     case {1: _, 2: _}:
...         ...
...     case {**rest}:
...         ...
... """), indent=4))
Module(
    body=[
        Match(
            subject=Name(id='x', ctx=Load()),
            cases=[
                match_case(
                    pattern=MatchMapping(
                        keys=[
                            Constant(value=1),
                            Constant(value=2)],
                        patterns=[
                            MatchAs(),
                            MatchAs()]),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))]),
                match_case(
                    pattern=MatchMapping(keys=[], patterns=[], rest='rest'),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))])])],
    type_ignores=[])
</pre> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.10.</span></p> </div> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.MatchClass">
<code>class ast.MatchClass(cls, patterns, kwd_attrs, kwd_patterns)</code> </dt> <dd>
<p>A match class pattern. <code>cls</code> is an expression giving the nominal class to be matched. <code>patterns</code> is a sequence of pattern nodes to be matched against the class defined sequence of pattern matching attributes. <code>kwd_attrs</code> is a sequence of additional attributes to be matched (specified as keyword arguments in the class pattern), <code>kwd_patterns</code> are the corresponding patterns (specified as keyword values in the class pattern).</p> <p>This pattern succeeds if the subject is an instance of the nominated class, all positional patterns match the corresponding class-defined attributes, and any specified keyword attributes match their corresponding pattern.</p> <p>Note: classes may define a property that returns self in order to match a pattern node against the instance being matched. Several builtin types are also matched that way, as described in the match statement documentation.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse("""
... match x:
...     case Point2D(0, 0):
...         ...
...     case Point3D(x=0, y=0, z=0):
...         ...
... """), indent=4))
Module(
    body=[
        Match(
            subject=Name(id='x', ctx=Load()),
            cases=[
                match_case(
                    pattern=MatchClass(
                        cls=Name(id='Point2D', ctx=Load()),
                        patterns=[
                            MatchValue(
                                value=Constant(value=0)),
                            MatchValue(
                                value=Constant(value=0))],
                        kwd_attrs=[],
                        kwd_patterns=[]),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))]),
                match_case(
                    pattern=MatchClass(
                        cls=Name(id='Point3D', ctx=Load()),
                        patterns=[],
                        kwd_attrs=[
                            'x',
                            'y',
                            'z'],
                        kwd_patterns=[
                            MatchValue(
                                value=Constant(value=0)),
                            MatchValue(
                                value=Constant(value=0)),
                            MatchValue(
                                value=Constant(value=0))]),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))])])],
    type_ignores=[])
</pre> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.10.</span></p> </div> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.MatchAs">
<code>class ast.MatchAs(pattern, name)</code> </dt> <dd>
<p>A match “as-pattern”, capture pattern or wildcard pattern. <code>pattern</code> contains the match pattern that the subject will be matched against. If the pattern is <code>None</code>, the node represents a capture pattern (i.e a bare name) and will always succeed.</p> <p>The <code>name</code> attribute contains the name that will be bound if the pattern is successful. If <code>name</code> is <code>None</code>, <code>pattern</code> must also be <code>None</code> and the node represents the wildcard pattern.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse("""
... match x:
...     case [x] as y:
...         ...
...     case _:
...         ...
... """), indent=4))
Module(
    body=[
        Match(
            subject=Name(id='x', ctx=Load()),
            cases=[
                match_case(
                    pattern=MatchAs(
                        pattern=MatchSequence(
                            patterns=[
                                MatchAs(name='x')]),
                        name='y'),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))]),
                match_case(
                    pattern=MatchAs(),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))])])],
    type_ignores=[])
</pre> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.10.</span></p> </div> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.MatchOr">
<code>class ast.MatchOr(patterns)</code> </dt> <dd>
<p>A match “or-pattern”. An or-pattern matches each of its subpatterns in turn to the subject, until one succeeds. The or-pattern is then deemed to succeed. If none of the subpatterns succeed the or-pattern fails. The <code>patterns</code> attribute contains a list of match pattern nodes that will be matched against the subject.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse("""
... match x:
...     case [x] | (y):
...         ...
... """), indent=4))
Module(
    body=[
        Match(
            subject=Name(id='x', ctx=Load()),
            cases=[
                match_case(
                    pattern=MatchOr(
                        patterns=[
                            MatchSequence(
                                patterns=[
                                    MatchAs(name='x')]),
                            MatchAs(name='y')]),
                    body=[
                        Expr(
                            value=Constant(value=Ellipsis))])])],
    type_ignores=[])
</pre> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.10.</span></p> </div> </dd>
</dl> </section> <section id="type-parameters"> <span id="ast-type-params"></span><h3>Type parameters</h3> <p><a class="reference internal" href="../reference/compound_stmts#type-params"><span class="std std-ref">Type parameters</span></a> can exist on classes, functions, and type aliases.</p> <dl class="py class"> <dt class="sig sig-object py" id="ast.TypeVar">
<code>class ast.TypeVar(name, bound)</code> </dt> <dd>
<p>A <a class="reference internal" href="typing#typing.TypeVar" title="typing.TypeVar"><code>typing.TypeVar</code></a>. <code>name</code> is the name of the type variable. <code>bound</code> is the bound or constraints, if any. If <code>bound</code> is a <a class="reference internal" href="#ast.Tuple" title="ast.Tuple"><code>Tuple</code></a>, it represents constraints; otherwise it represents the bound.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse("type Alias[T: int] = list[T]"), indent=4))
Module(
    body=[
        TypeAlias(
            name=Name(id='Alias', ctx=Store()),
            type_params=[
                TypeVar(
                    name='T',
                    bound=Name(id='int', ctx=Load()))],
            value=Subscript(
                value=Name(id='list', ctx=Load()),
                slice=Name(id='T', ctx=Load()),
                ctx=Load()))],
    type_ignores=[])
</pre> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.12.</span></p> </div> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.ParamSpec">
<code>class ast.ParamSpec(name)</code> </dt> <dd>
<p>A <a class="reference internal" href="typing#typing.ParamSpec" title="typing.ParamSpec"><code>typing.ParamSpec</code></a>. <code>name</code> is the name of the parameter specification.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse("type Alias[**P] = Callable[P, int]"), indent=4))
Module(
    body=[
        TypeAlias(
            name=Name(id='Alias', ctx=Store()),
            type_params=[
                ParamSpec(name='P')],
            value=Subscript(
                value=Name(id='Callable', ctx=Load()),
                slice=Tuple(
                    elts=[
                        Name(id='P', ctx=Load()),
                        Name(id='int', ctx=Load())],
                    ctx=Load()),
                ctx=Load()))],
    type_ignores=[])
</pre> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.12.</span></p> </div> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.TypeVarTuple">
<code>class ast.TypeVarTuple(name)</code> </dt> <dd>
<p>A <a class="reference internal" href="typing#typing.TypeVarTuple" title="typing.TypeVarTuple"><code>typing.TypeVarTuple</code></a>. <code>name</code> is the name of the type variable tuple.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse("type Alias[*Ts] = tuple[*Ts]"), indent=4))
Module(
    body=[
        TypeAlias(
            name=Name(id='Alias', ctx=Store()),
            type_params=[
                TypeVarTuple(name='Ts')],
            value=Subscript(
                value=Name(id='tuple', ctx=Load()),
                slice=Tuple(
                    elts=[
                        Starred(
                            value=Name(id='Ts', ctx=Load()),
                            ctx=Load())],
                    ctx=Load()),
                ctx=Load()))],
    type_ignores=[])
</pre> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.12.</span></p> </div> </dd>
</dl> </section> <section id="function-and-class-definitions"> <h3>Function and class definitions</h3> <dl class="py class"> <dt class="sig sig-object py" id="ast.FunctionDef">
<code>class ast.FunctionDef(name, args, body, decorator_list, returns, type_comment, type_params)</code> </dt> <dd>
<p>A function definition.</p> <ul class="simple"> <li>
<code>name</code> is a raw string of the function name.</li> <li>
<code>args</code> is an <a class="reference internal" href="#ast.arguments" title="ast.arguments"><code>arguments</code></a> node.</li> <li>
<code>body</code> is the list of nodes inside the function.</li> <li>
<code>decorator_list</code> is the list of decorators to be applied, stored outermost first (i.e. the first in the list will be applied last).</li> <li>
<code>returns</code> is the return annotation.</li> <li>
<code>type_params</code> is a list of <a class="reference internal" href="#ast-type-params"><span class="std std-ref">type parameters</span></a>.</li> </ul> <dl class="py attribute"> <dt class="sig sig-object py" id="ast.FunctionDef.type_comment">
<code>type_comment</code> </dt> <dd>
<p><code>type_comment</code> is an optional string with the type annotation as a comment.</p> </dd>
</dl> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.12: </span>Added <code>type_params</code>.</p> </div> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.Lambda">
<code>class ast.Lambda(args, body)</code> </dt> <dd>
<p><code>lambda</code> is a minimal function definition that can be used inside an expression. Unlike <a class="reference internal" href="#ast.FunctionDef" title="ast.FunctionDef"><code>FunctionDef</code></a>, <code>body</code> holds a single node.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('lambda x,y: ...'), indent=4))
Module(
    body=[
        Expr(
            value=Lambda(
                args=arguments(
                    posonlyargs=[],
                    args=[
                        arg(arg='x'),
                        arg(arg='y')],
                    kwonlyargs=[],
                    kw_defaults=[],
                    defaults=[]),
                body=Constant(value=Ellipsis)))],
    type_ignores=[])
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.arguments">
<code>class ast.arguments(posonlyargs, args, vararg, kwonlyargs, kw_defaults, kwarg, defaults)</code> </dt> <dd>
<p>The arguments for a function.</p> <ul class="simple"> <li>
<code>posonlyargs</code>, <code>args</code> and <code>kwonlyargs</code> are lists of <a class="reference internal" href="#ast.arg" title="ast.arg"><code>arg</code></a> nodes.</li> <li>
<code>vararg</code> and <code>kwarg</code> are single <a class="reference internal" href="#ast.arg" title="ast.arg"><code>arg</code></a> nodes, referring to the <code>*args, **kwargs</code> parameters.</li> <li>
<code>kw_defaults</code> is a list of default values for keyword-only arguments. If one is <code>None</code>, the corresponding argument is required.</li> <li>
<code>defaults</code> is a list of default values for arguments that can be passed positionally. If there are fewer defaults, they correspond to the last n arguments.</li> </ul> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.arg">
<code>class ast.arg(arg, annotation, type_comment)</code> </dt> <dd>
<p>A single argument in a list. <code>arg</code> is a raw string of the argument name; <code>annotation</code> is its annotation, such as a <a class="reference internal" href="#ast.Name" title="ast.Name"><code>Name</code></a> node.</p> <dl class="py attribute"> <dt class="sig sig-object py" id="ast.arg.type_comment">
<code>type_comment</code> </dt> <dd>
<p><code>type_comment</code> is an optional string with the type annotation as a comment</p> </dd>
</dl> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse("""\
... @decorator1
... @decorator2
... def f(a: 'annotation', b=1, c=2, *d, e, f=3, **g) -&gt; 'return annotation':
...     pass
... """), indent=4))
Module(
    body=[
        FunctionDef(
            name='f',
            args=arguments(
                posonlyargs=[],
                args=[
                    arg(
                        arg='a',
                        annotation=Constant(value='annotation')),
                    arg(arg='b'),
                    arg(arg='c')],
                vararg=arg(arg='d'),
                kwonlyargs=[
                    arg(arg='e'),
                    arg(arg='f')],
                kw_defaults=[
                    None,
                    Constant(value=3)],
                kwarg=arg(arg='g'),
                defaults=[
                    Constant(value=1),
                    Constant(value=2)]),
            body=[
                Pass()],
            decorator_list=[
                Name(id='decorator1', ctx=Load()),
                Name(id='decorator2', ctx=Load())],
            returns=Constant(value='return annotation'),
            type_params=[])],
    type_ignores=[])
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.Return">
<code>class ast.Return(value)</code> </dt> <dd>
<p>A <code>return</code> statement.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('return 4'), indent=4))
Module(
    body=[
        Return(
            value=Constant(value=4))],
    type_ignores=[])
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.Yield">
<code>class ast.Yield(value)</code> </dt> <dt class="sig sig-object py" id="ast.YieldFrom">
<code>class ast.YieldFrom(value)</code> </dt> <dd>
<p>A <code>yield</code> or <code>yield from</code> expression. Because these are expressions, they must be wrapped in a <a class="reference internal" href="#ast.Expr" title="ast.Expr"><code>Expr</code></a> node if the value sent back is not used.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('yield x'), indent=4))
Module(
    body=[
        Expr(
            value=Yield(
                value=Name(id='x', ctx=Load())))],
    type_ignores=[])

&gt;&gt;&gt; print(ast.dump(ast.parse('yield from x'), indent=4))
Module(
    body=[
        Expr(
            value=YieldFrom(
                value=Name(id='x', ctx=Load())))],
    type_ignores=[])
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.Global">
<code>class ast.Global(names)</code> </dt> <dt class="sig sig-object py" id="ast.Nonlocal">
<code>class ast.Nonlocal(names)</code> </dt> <dd>
<p><code>global</code> and <code>nonlocal</code> statements. <code>names</code> is a list of raw strings.</p> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse('global x,y,z'), indent=4))
Module(
    body=[
        Global(
            names=[
                'x',
                'y',
                'z'])],
    type_ignores=[])

&gt;&gt;&gt; print(ast.dump(ast.parse('nonlocal x,y,z'), indent=4))
Module(
    body=[
        Nonlocal(
            names=[
                'x',
                'y',
                'z'])],
    type_ignores=[])
</pre> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.ClassDef">
<code>class ast.ClassDef(name, bases, keywords, body, decorator_list, type_params)</code> </dt> <dd>
<p>A class definition.</p> <ul class="simple"> <li>
<code>name</code> is a raw string for the class name</li> <li>
<code>bases</code> is a list of nodes for explicitly specified base classes.</li> <li>
<code>keywords</code> is a list of <a class="reference internal" href="#ast.keyword" title="ast.keyword"><code>keyword</code></a> nodes, principally for ‘metaclass’. Other keywords will be passed to the metaclass, as per <a class="reference external" href="https://peps.python.org/pep-3115/">PEP-3115</a>.</li> <li>
<code>body</code> is a list of nodes representing the code within the class definition.</li> <li>
<code>decorator_list</code> is a list of nodes, as in <a class="reference internal" href="#ast.FunctionDef" title="ast.FunctionDef"><code>FunctionDef</code></a>.</li> <li>
<code>type_params</code> is a list of <a class="reference internal" href="#ast-type-params"><span class="std std-ref">type parameters</span></a>.</li> </ul> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse("""\
... @decorator1
... @decorator2
... class Foo(base1, base2, metaclass=meta):
...     pass
... """), indent=4))
Module(
    body=[
        ClassDef(
            name='Foo',
            bases=[
                Name(id='base1', ctx=Load()),
                Name(id='base2', ctx=Load())],
            keywords=[
                keyword(
                    arg='metaclass',
                    value=Name(id='meta', ctx=Load()))],
            body=[
                Pass()],
            decorator_list=[
                Name(id='decorator1', ctx=Load()),
                Name(id='decorator2', ctx=Load())],
            type_params=[])],
    type_ignores=[])
</pre> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.12: </span>Added <code>type_params</code>.</p> </div> </dd>
</dl> </section> <section id="async-and-await"> <h3>Async and await</h3> <dl class="py class"> <dt class="sig sig-object py" id="ast.AsyncFunctionDef">
<code>class ast.AsyncFunctionDef(name, args, body, decorator_list, returns, type_comment, type_params)</code> </dt> <dd>
<p>An <code>async def</code> function definition. Has the same fields as <a class="reference internal" href="#ast.FunctionDef" title="ast.FunctionDef"><code>FunctionDef</code></a>.</p> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.12: </span>Added <code>type_params</code>.</p> </div> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.Await">
<code>class ast.Await(value)</code> </dt> <dd>
<p>An <code>await</code> expression. <code>value</code> is what it waits for. Only valid in the body of an <a class="reference internal" href="#ast.AsyncFunctionDef" title="ast.AsyncFunctionDef"><code>AsyncFunctionDef</code></a>.</p> </dd>
</dl> <pre data-language="pycon3">&gt;&gt;&gt; print(ast.dump(ast.parse("""\
... async def f():
...     await other_func()
... """), indent=4))
Module(
    body=[
        AsyncFunctionDef(
            name='f',
            args=arguments(
                posonlyargs=[],
                args=[],
                kwonlyargs=[],
                kw_defaults=[],
                defaults=[]),
            body=[
                Expr(
                    value=Await(
                        value=Call(
                            func=Name(id='other_func', ctx=Load()),
                            args=[],
                            keywords=[])))],
            decorator_list=[],
            type_params=[])],
    type_ignores=[])
</pre> <dl class="py class"> <dt class="sig sig-object py" id="ast.AsyncFor">
<code>class ast.AsyncFor(target, iter, body, orelse, type_comment)</code> </dt> <dt class="sig sig-object py" id="ast.AsyncWith">
<code>class ast.AsyncWith(items, body, type_comment)</code> </dt> <dd>
<p><code>async for</code> loops and <code>async with</code> context managers. They have the same fields as <a class="reference internal" href="#ast.For" title="ast.For"><code>For</code></a> and <a class="reference internal" href="#ast.With" title="ast.With"><code>With</code></a>, respectively. Only valid in the body of an <a class="reference internal" href="#ast.AsyncFunctionDef" title="ast.AsyncFunctionDef"><code>AsyncFunctionDef</code></a>.</p> </dd>
</dl> <div class="admonition note"> <p class="admonition-title">Note</p> <p>When a string is parsed by <a class="reference internal" href="#ast.parse" title="ast.parse"><code>ast.parse()</code></a>, operator nodes (subclasses of <code>ast.operator</code>, <code>ast.unaryop</code>, <code>ast.cmpop</code>, <code>ast.boolop</code> and <code>ast.expr_context</code>) on the returned tree will be singletons. Changes to one will be reflected in all other occurrences of the same value (e.g. <a class="reference internal" href="#ast.Add" title="ast.Add"><code>ast.Add</code></a>).</p> </div> </section> </section> <section id="ast-helpers"> <h2>ast Helpers</h2> <p>Apart from the node classes, the <a class="reference internal" href="#module-ast" title="ast: Abstract Syntax Tree classes and manipulation."><code>ast</code></a> module defines these utility functions and classes for traversing abstract syntax trees:</p> <dl class="py function"> <dt class="sig sig-object py" id="ast.parse">
<code>ast.parse(source, filename='&lt;unknown&gt;', mode='exec', *, type_comments=False, feature_version=None)</code> </dt> <dd>
<p>Parse the source into an AST node. Equivalent to <code>compile(source,
filename, mode, ast.PyCF_ONLY_AST)</code>.</p> <p>If <code>type_comments=True</code> is given, the parser is modified to check and return type comments as specified by <span class="target" id="index-3"></span><a class="pep reference external" href="https://peps.python.org/pep-0484/"><strong>PEP 484</strong></a> and <span class="target" id="index-4"></span><a class="pep reference external" href="https://peps.python.org/pep-0526/"><strong>PEP 526</strong></a>. This is equivalent to adding <a class="reference internal" href="#ast.PyCF_TYPE_COMMENTS" title="ast.PyCF_TYPE_COMMENTS"><code>ast.PyCF_TYPE_COMMENTS</code></a> to the flags passed to <a class="reference internal" href="functions#compile" title="compile"><code>compile()</code></a>. This will report syntax errors for misplaced type comments. Without this flag, type comments will be ignored, and the <code>type_comment</code> field on selected AST nodes will always be <code>None</code>. In addition, the locations of <code># type:
ignore</code> comments will be returned as the <code>type_ignores</code> attribute of <a class="reference internal" href="#ast.Module" title="ast.Module"><code>Module</code></a> (otherwise it is always an empty list).</p> <p>In addition, if <code>mode</code> is <code>'func_type'</code>, the input syntax is modified to correspond to <span class="target" id="index-5"></span><a class="pep reference external" href="https://peps.python.org/pep-0484/"><strong>PEP 484</strong></a> “signature type comments”, e.g. <code>(str, int) -&gt; List[str]</code>.</p> <p>Also, setting <code>feature_version</code> to a tuple <code>(major, minor)</code> will attempt to parse using that Python version’s grammar. Currently <code>major</code> must equal to <code>3</code>. For example, setting <code>feature_version=(3, 4)</code> will allow the use of <code>async</code> and <code>await</code> as variable names. The lowest supported version is <code>(3, 4)</code>; the highest is <code>sys.version_info[0:2]</code>.</p> <p>If source contains a null character (’0’), <a class="reference internal" href="exceptions#ValueError" title="ValueError"><code>ValueError</code></a> is raised.</p> <div class="admonition warning"> <p class="admonition-title">Warning</p> <p>Note that successfully parsing source code into an AST object doesn’t guarantee that the source code provided is valid Python code that can be executed as the compilation step can raise further <a class="reference internal" href="exceptions#SyntaxError" title="SyntaxError"><code>SyntaxError</code></a> exceptions. For instance, the source <code>return 42</code> generates a valid AST node for a return statement, but it cannot be compiled alone (it needs to be inside a function node).</p> <p>In particular, <a class="reference internal" href="#ast.parse" title="ast.parse"><code>ast.parse()</code></a> won’t do any scoping checks, which the compilation step does.</p> </div> <div class="admonition warning"> <p class="admonition-title">Warning</p> <p>It is possible to crash the Python interpreter with a sufficiently large/complex string due to stack depth limitations in Python’s AST compiler.</p> </div> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.8: </span>Added <code>type_comments</code>, <code>mode='func_type'</code> and <code>feature_version</code>.</p> </div> </dd>
</dl> <dl class="py function"> <dt class="sig sig-object py" id="ast.unparse">
<code>ast.unparse(ast_obj)</code> </dt> <dd>
<p>Unparse an <a class="reference internal" href="#ast.AST" title="ast.AST"><code>ast.AST</code></a> object and generate a string with code that would produce an equivalent <a class="reference internal" href="#ast.AST" title="ast.AST"><code>ast.AST</code></a> object if parsed back with <a class="reference internal" href="#ast.parse" title="ast.parse"><code>ast.parse()</code></a>.</p> <div class="admonition warning"> <p class="admonition-title">Warning</p> <p>The produced code string will not necessarily be equal to the original code that generated the <a class="reference internal" href="#ast.AST" title="ast.AST"><code>ast.AST</code></a> object (without any compiler optimizations, such as constant tuples/frozensets).</p> </div> <div class="admonition warning"> <p class="admonition-title">Warning</p> <p>Trying to unparse a highly complex expression would result with <a class="reference internal" href="exceptions#RecursionError" title="RecursionError"><code>RecursionError</code></a>.</p> </div> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.9.</span></p> </div> </dd>
</dl> <dl class="py function"> <dt class="sig sig-object py" id="ast.literal_eval">
<code>ast.literal_eval(node_or_string)</code> </dt> <dd>
<p>Evaluate an expression node or a string containing only a Python literal or container display. The string or node provided may only consist of the following Python literal structures: strings, bytes, numbers, tuples, lists, dicts, sets, booleans, <code>None</code> and <code>Ellipsis</code>.</p> <p>This can be used for evaluating strings containing Python values without the need to parse the values oneself. It is not capable of evaluating arbitrarily complex expressions, for example involving operators or indexing.</p> <p>This function had been documented as “safe” in the past without defining what that meant. That was misleading. This is specifically designed not to execute Python code, unlike the more general <a class="reference internal" href="functions#eval" title="eval"><code>eval()</code></a>. There is no namespace, no name lookups, or ability to call out. But it is not free from attack: A relatively small input can lead to memory exhaustion or to C stack exhaustion, crashing the process. There is also the possibility for excessive CPU consumption denial of service on some inputs. Calling it on untrusted data is thus not recommended.</p> <div class="admonition warning"> <p class="admonition-title">Warning</p> <p>It is possible to crash the Python interpreter due to stack depth limitations in Python’s AST compiler.</p> <p>It can raise <a class="reference internal" href="exceptions#ValueError" title="ValueError"><code>ValueError</code></a>, <a class="reference internal" href="exceptions#TypeError" title="TypeError"><code>TypeError</code></a>, <a class="reference internal" href="exceptions#SyntaxError" title="SyntaxError"><code>SyntaxError</code></a>, <a class="reference internal" href="exceptions#MemoryError" title="MemoryError"><code>MemoryError</code></a> and <a class="reference internal" href="exceptions#RecursionError" title="RecursionError"><code>RecursionError</code></a> depending on the malformed input.</p> </div> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.2: </span>Now allows bytes and set literals.</p> </div> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.9: </span>Now supports creating empty sets with <code>'set()'</code>.</p> </div> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.10: </span>For string inputs, leading spaces and tabs are now stripped.</p> </div> </dd>
</dl> <dl class="py function"> <dt class="sig sig-object py" id="ast.get_docstring">
<code>ast.get_docstring(node, clean=True)</code> </dt> <dd>
<p>Return the docstring of the given <em>node</em> (which must be a <a class="reference internal" href="#ast.FunctionDef" title="ast.FunctionDef"><code>FunctionDef</code></a>, <a class="reference internal" href="#ast.AsyncFunctionDef" title="ast.AsyncFunctionDef"><code>AsyncFunctionDef</code></a>, <a class="reference internal" href="#ast.ClassDef" title="ast.ClassDef"><code>ClassDef</code></a>, or <a class="reference internal" href="#ast.Module" title="ast.Module"><code>Module</code></a> node), or <code>None</code> if it has no docstring. If <em>clean</em> is true, clean up the docstring’s indentation with <a class="reference internal" href="inspect#inspect.cleandoc" title="inspect.cleandoc"><code>inspect.cleandoc()</code></a>.</p> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.5: </span><a class="reference internal" href="#ast.AsyncFunctionDef" title="ast.AsyncFunctionDef"><code>AsyncFunctionDef</code></a> is now supported.</p> </div> </dd>
</dl> <dl class="py function"> <dt class="sig sig-object py" id="ast.get_source_segment">
<code>ast.get_source_segment(source, node, *, padded=False)</code> </dt> <dd>
<p>Get source code segment of the <em>source</em> that generated <em>node</em>. If some location information (<a class="reference internal" href="#ast.AST.lineno" title="ast.AST.lineno"><code>lineno</code></a>, <a class="reference internal" href="#ast.AST.end_lineno" title="ast.AST.end_lineno"><code>end_lineno</code></a>, <a class="reference internal" href="#ast.AST.col_offset" title="ast.AST.col_offset"><code>col_offset</code></a>, or <a class="reference internal" href="#ast.AST.end_col_offset" title="ast.AST.end_col_offset"><code>end_col_offset</code></a>) is missing, return <code>None</code>.</p> <p>If <em>padded</em> is <code>True</code>, the first line of a multi-line statement will be padded with spaces to match its original position.</p> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.8.</span></p> </div> </dd>
</dl> <dl class="py function"> <dt class="sig sig-object py" id="ast.fix_missing_locations">
<code>ast.fix_missing_locations(node)</code> </dt> <dd>
<p>When you compile a node tree with <a class="reference internal" href="functions#compile" title="compile"><code>compile()</code></a>, the compiler expects <a class="reference internal" href="#ast.AST.lineno" title="ast.AST.lineno"><code>lineno</code></a> and <a class="reference internal" href="#ast.AST.col_offset" title="ast.AST.col_offset"><code>col_offset</code></a> attributes for every node that supports them. This is rather tedious to fill in for generated nodes, so this helper adds these attributes recursively where not already set, by setting them to the values of the parent node. It works recursively starting at <em>node</em>.</p> </dd>
</dl> <dl class="py function"> <dt class="sig sig-object py" id="ast.increment_lineno">
<code>ast.increment_lineno(node, n=1)</code> </dt> <dd>
<p>Increment the line number and end line number of each node in the tree starting at <em>node</em> by <em>n</em>. This is useful to “move code” to a different location in a file.</p> </dd>
</dl> <dl class="py function"> <dt class="sig sig-object py" id="ast.copy_location">
<code>ast.copy_location(new_node, old_node)</code> </dt> <dd>
<p>Copy source location (<a class="reference internal" href="#ast.AST.lineno" title="ast.AST.lineno"><code>lineno</code></a>, <a class="reference internal" href="#ast.AST.col_offset" title="ast.AST.col_offset"><code>col_offset</code></a>, <a class="reference internal" href="#ast.AST.end_lineno" title="ast.AST.end_lineno"><code>end_lineno</code></a>, and <a class="reference internal" href="#ast.AST.end_col_offset" title="ast.AST.end_col_offset"><code>end_col_offset</code></a>) from <em>old_node</em> to <em>new_node</em> if possible, and return <em>new_node</em>.</p> </dd>
</dl> <dl class="py function"> <dt class="sig sig-object py" id="ast.iter_fields">
<code>ast.iter_fields(node)</code> </dt> <dd>
<p>Yield a tuple of <code>(fieldname, value)</code> for each field in <code>node._fields</code> that is present on <em>node</em>.</p> </dd>
</dl> <dl class="py function"> <dt class="sig sig-object py" id="ast.iter_child_nodes">
<code>ast.iter_child_nodes(node)</code> </dt> <dd>
<p>Yield all direct child nodes of <em>node</em>, that is, all fields that are nodes and all items of fields that are lists of nodes.</p> </dd>
</dl> <dl class="py function"> <dt class="sig sig-object py" id="ast.walk">
<code>ast.walk(node)</code> </dt> <dd>
<p>Recursively yield all descendant nodes in the tree starting at <em>node</em> (including <em>node</em> itself), in no specified order. This is useful if you only want to modify nodes in place and don’t care about the context.</p> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.NodeVisitor">
<code>class ast.NodeVisitor</code> </dt> <dd>
<p>A node visitor base class that walks the abstract syntax tree and calls a visitor function for every node found. This function may return a value which is forwarded by the <a class="reference internal" href="#ast.NodeVisitor.visit" title="ast.NodeVisitor.visit"><code>visit()</code></a> method.</p> <p>This class is meant to be subclassed, with the subclass adding visitor methods.</p> <dl class="py method"> <dt class="sig sig-object py" id="ast.NodeVisitor.visit">
<code>visit(node)</code> </dt> <dd>
<p>Visit a node. The default implementation calls the method called <code>self.visit_<em>classname</em></code> where <em>classname</em> is the name of the node class, or <a class="reference internal" href="#ast.NodeVisitor.generic_visit" title="ast.NodeVisitor.generic_visit"><code>generic_visit()</code></a> if that method doesn’t exist.</p> </dd>
</dl> <dl class="py method"> <dt class="sig sig-object py" id="ast.NodeVisitor.generic_visit">
<code>generic_visit(node)</code> </dt> <dd>
<p>This visitor calls <a class="reference internal" href="#ast.NodeVisitor.visit" title="ast.NodeVisitor.visit"><code>visit()</code></a> on all children of the node.</p> <p>Note that child nodes of nodes that have a custom visitor method won’t be visited unless the visitor calls <a class="reference internal" href="#ast.NodeVisitor.generic_visit" title="ast.NodeVisitor.generic_visit"><code>generic_visit()</code></a> or visits them itself.</p> </dd>
</dl> <dl class="py method"> <dt class="sig sig-object py" id="ast.NodeVisitor.visit_Constant">
<code>visit_Constant(node)</code> </dt> <dd>
<p>Handles all constant nodes.</p> </dd>
</dl> <p>Don’t use the <a class="reference internal" href="#ast.NodeVisitor" title="ast.NodeVisitor"><code>NodeVisitor</code></a> if you want to apply changes to nodes during traversal. For this a special visitor exists (<a class="reference internal" href="#ast.NodeTransformer" title="ast.NodeTransformer"><code>NodeTransformer</code></a>) that allows modifications.</p> <div class="deprecated"> <p><span class="versionmodified deprecated">Deprecated since version 3.8: </span>Methods <code>visit_Num()</code>, <code>visit_Str()</code>, <code>visit_Bytes()</code>, <code>visit_NameConstant()</code> and <code>visit_Ellipsis()</code> are deprecated now and will not be called in future Python versions. Add the <a class="reference internal" href="#ast.NodeVisitor.visit_Constant" title="ast.NodeVisitor.visit_Constant"><code>visit_Constant()</code></a> method to handle all constant nodes.</p> </div> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="ast.NodeTransformer">
<code>class ast.NodeTransformer</code> </dt> <dd>
<p>A <a class="reference internal" href="#ast.NodeVisitor" title="ast.NodeVisitor"><code>NodeVisitor</code></a> subclass that walks the abstract syntax tree and allows modification of nodes.</p> <p>The <a class="reference internal" href="#ast.NodeTransformer" title="ast.NodeTransformer"><code>NodeTransformer</code></a> will walk the AST and use the return value of the visitor methods to replace or remove the old node. If the return value of the visitor method is <code>None</code>, the node will be removed from its location, otherwise it is replaced with the return value. The return value may be the original node in which case no replacement takes place.</p> <p>Here is an example transformer that rewrites all occurrences of name lookups (<code>foo</code>) to <code>data['foo']</code>:</p> <pre data-language="python">class RewriteName(NodeTransformer):

    def visit_Name(self, node):
        return Subscript(
            value=Name(id='data', ctx=Load()),
            slice=Constant(value=node.id),
            ctx=node.ctx
        )
</pre> <p>Keep in mind that if the node you’re operating on has child nodes you must either transform the child nodes yourself or call the <a class="reference internal" href="#ast.NodeVisitor.generic_visit" title="ast.NodeVisitor.generic_visit"><code>generic_visit()</code></a> method for the node first.</p> <p>For nodes that were part of a collection of statements (that applies to all statement nodes), the visitor may also return a list of nodes rather than just a single node.</p> <p>If <a class="reference internal" href="#ast.NodeTransformer" title="ast.NodeTransformer"><code>NodeTransformer</code></a> introduces new nodes (that weren’t part of original tree) without giving them location information (such as <a class="reference internal" href="#ast.AST.lineno" title="ast.AST.lineno"><code>lineno</code></a>), <a class="reference internal" href="#ast.fix_missing_locations" title="ast.fix_missing_locations"><code>fix_missing_locations()</code></a> should be called with the new sub-tree to recalculate the location information:</p> <pre data-language="python">tree = ast.parse('foo', mode='eval')
new_tree = fix_missing_locations(RewriteName().visit(tree))
</pre> <p>Usually you use the transformer like this:</p> <pre data-language="python">node = YourTransformer().visit(node)
</pre> </dd>
</dl> <dl class="py function"> <dt class="sig sig-object py" id="ast.dump">
<code>ast.dump(node, annotate_fields=True, include_attributes=False, *, indent=None)</code> </dt> <dd>
<p>Return a formatted dump of the tree in <em>node</em>. This is mainly useful for debugging purposes. If <em>annotate_fields</em> is true (by default), the returned string will show the names and the values for fields. If <em>annotate_fields</em> is false, the result string will be more compact by omitting unambiguous field names. Attributes such as line numbers and column offsets are not dumped by default. If this is wanted, <em>include_attributes</em> can be set to true.</p> <p>If <em>indent</em> is a non-negative integer or string, then the tree will be pretty-printed with that indent level. An indent level of 0, negative, or <code>""</code> will only insert newlines. <code>None</code> (the default) selects the single line representation. Using a positive integer indent indents that many spaces per level. If <em>indent</em> is a string (such as <code>"\t"</code>), that string is used to indent each level.</p> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.9: </span>Added the <em>indent</em> option.</p> </div> </dd>
</dl> </section> <section id="compiler-flags"> <span id="ast-compiler-flags"></span><h2>Compiler Flags</h2> <p>The following flags may be passed to <a class="reference internal" href="functions#compile" title="compile"><code>compile()</code></a> in order to change effects on the compilation of a program:</p> <dl class="py data"> <dt class="sig sig-object py" id="ast.PyCF_ALLOW_TOP_LEVEL_AWAIT">
<code>ast.PyCF_ALLOW_TOP_LEVEL_AWAIT</code> </dt> <dd>
<p>Enables support for top-level <code>await</code>, <code>async for</code>, <code>async with</code> and async comprehensions.</p> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.8.</span></p> </div> </dd>
</dl> <dl class="py data"> <dt class="sig sig-object py" id="ast.PyCF_ONLY_AST">
<code>ast.PyCF_ONLY_AST</code> </dt> <dd>
<p>Generates and returns an abstract syntax tree instead of returning a compiled code object.</p> </dd>
</dl> <dl class="py data"> <dt class="sig sig-object py" id="ast.PyCF_TYPE_COMMENTS">
<code>ast.PyCF_TYPE_COMMENTS</code> </dt> <dd>
<p>Enables support for <span class="target" id="index-6"></span><a class="pep reference external" href="https://peps.python.org/pep-0484/"><strong>PEP 484</strong></a> and <span class="target" id="index-7"></span><a class="pep reference external" href="https://peps.python.org/pep-0526/"><strong>PEP 526</strong></a> style type comments (<code># type: &lt;type&gt;</code>, <code># type: ignore &lt;stuff&gt;</code>).</p> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.8.</span></p> </div> </dd>
</dl> </section> <section id="command-line-usage"> <span id="ast-cli"></span><h2>Command-Line Usage</h2> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.9.</span></p> </div> <p>The <a class="reference internal" href="#module-ast" title="ast: Abstract Syntax Tree classes and manipulation."><code>ast</code></a> module can be executed as a script from the command line. It is as simple as:</p> <pre data-language="sh">python -m ast [-m &lt;mode&gt;] [-a] [infile]
</pre> <p>The following options are accepted:</p> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-ast-h">
<code>-h, --help</code> </dt> <dd>
<p>Show the help message and exit.</p> </dd>
</dl> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-ast-m">
<code>-m &lt;mode&gt;</code> </dt> <dt class="sig sig-object std" id="cmdoption-ast-mode">
<code>--mode &lt;mode&gt;</code> </dt> <dd>
<p>Specify what kind of code must be compiled, like the <em>mode</em> argument in <a class="reference internal" href="#ast.parse" title="ast.parse"><code>parse()</code></a>.</p> </dd>
</dl> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-ast-no-type-comments">
<code>--no-type-comments</code> </dt> <dd>
<p>Don’t parse type comments.</p> </dd>
</dl> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-ast-a">
<code>-a, --include-attributes</code> </dt> <dd>
<p>Include attributes such as line numbers and column offsets.</p> </dd>
</dl> <dl class="std option"> <dt class="sig sig-object std" id="cmdoption-ast-i">
<code>-i &lt;indent&gt;</code> </dt> <dt class="sig sig-object std" id="cmdoption-ast-indent">
<code>--indent &lt;indent&gt;</code> </dt> <dd>
<p>Indentation of nodes in AST (number of spaces).</p> </dd>
</dl> <p>If <code>infile</code> is specified its contents are parsed to AST and dumped to stdout. Otherwise, the content is read from stdin.</p> <div class="admonition seealso"> <p class="admonition-title">See also</p> <p><a class="reference external" href="https://greentreesnakes.readthedocs.io/">Green Tree Snakes</a>, an external documentation resource, has good details on working with Python ASTs.</p> <p><a class="reference external" href="https://asttokens.readthedocs.io/en/latest/user-guide.html">ASTTokens</a> annotates Python ASTs with the positions of tokens and text in the source code that generated them. This is helpful for tools that make source code transformations.</p> <p><a class="reference external" href="https://leoeditor.com/appendices.html#leoast-py">leoAst.py</a> unifies the token-based and parse-tree-based views of python programs by inserting two-way links between tokens and ast nodes.</p> <p><a class="reference external" href="https://libcst.readthedocs.io/">LibCST</a> parses code as a Concrete Syntax Tree that looks like an ast tree and keeps all formatting details. It’s useful for building automated refactoring (codemod) applications and linters.</p> <p><a class="reference external" href="https://parso.readthedocs.io">Parso</a> is a Python parser that supports error recovery and round-trip parsing for different Python versions (in multiple Python versions). Parso is also able to list multiple syntax errors in your python file.</p> </div> </section> <div class="_attribution">
  <p class="_attribution-p">
    &copy; 2001&ndash;2023 Python Software Foundation<br>Licensed under the PSF License.<br>
    <a href="https://docs.python.org/3.12/library/ast.html" class="_attribution-link">https://docs.python.org/3.12/library/ast.html</a>
  </p>
</div>