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<span id="bz2-support-for-bzip2-compression"></span><h1>bz2 — Support for bzip2 compression</h1> <p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.12/Lib/bz2.py">Lib/bz2.py</a></p> <p>This module provides a comprehensive interface for compressing and decompressing data using the bzip2 compression algorithm.</p> <p>The <a class="reference internal" href="#module-bz2" title="bz2: Interfaces for bzip2 compression and decompression."><code>bz2</code></a> module contains:</p> <ul class="simple"> <li>The <a class="reference internal" href="#bz2.open" title="bz2.open"><code>open()</code></a> function and <a class="reference internal" href="#bz2.BZ2File" title="bz2.BZ2File"><code>BZ2File</code></a> class for reading and writing compressed files.</li> <li>The <a class="reference internal" href="#bz2.BZ2Compressor" title="bz2.BZ2Compressor"><code>BZ2Compressor</code></a> and <a class="reference internal" href="#bz2.BZ2Decompressor" title="bz2.BZ2Decompressor"><code>BZ2Decompressor</code></a> classes for incremental (de)compression.</li> <li>The <a class="reference internal" href="#bz2.compress" title="bz2.compress"><code>compress()</code></a> and <a class="reference internal" href="#bz2.decompress" title="bz2.decompress"><code>decompress()</code></a> functions for one-shot (de)compression.</li> </ul> <section id="de-compression-of-files"> <h2>(De)compression of files</h2> <dl class="py function"> <dt class="sig sig-object py" id="bz2.open">
<code>bz2.open(filename, mode='rb', compresslevel=9, encoding=None, errors=None, newline=None)</code> </dt> <dd>
<p>Open a bzip2-compressed file in binary or text mode, returning a <a class="reference internal" href="../glossary#term-file-object"><span class="xref std std-term">file object</span></a>.</p> <p>As with the constructor for <a class="reference internal" href="#bz2.BZ2File" title="bz2.BZ2File"><code>BZ2File</code></a>, the <em>filename</em> argument can be an actual filename (a <a class="reference internal" href="stdtypes#str" title="str"><code>str</code></a> or <a class="reference internal" href="stdtypes#bytes" title="bytes"><code>bytes</code></a> object), or an existing file object to read from or write to.</p> <p>The <em>mode</em> argument can be any of <code>'r'</code>, <code>'rb'</code>, <code>'w'</code>, <code>'wb'</code>, <code>'x'</code>, <code>'xb'</code>, <code>'a'</code> or <code>'ab'</code> for binary mode, or <code>'rt'</code>, <code>'wt'</code>, <code>'xt'</code>, or <code>'at'</code> for text mode. The default is <code>'rb'</code>.</p> <p>The <em>compresslevel</em> argument is an integer from 1 to 9, as for the <a class="reference internal" href="#bz2.BZ2File" title="bz2.BZ2File"><code>BZ2File</code></a> constructor.</p> <p>For binary mode, this function is equivalent to the <a class="reference internal" href="#bz2.BZ2File" title="bz2.BZ2File"><code>BZ2File</code></a> constructor: <code>BZ2File(filename, mode, compresslevel=compresslevel)</code>. In this case, the <em>encoding</em>, <em>errors</em> and <em>newline</em> arguments must not be provided.</p> <p>For text mode, a <a class="reference internal" href="#bz2.BZ2File" title="bz2.BZ2File"><code>BZ2File</code></a> object is created, and wrapped in an <a class="reference internal" href="io#io.TextIOWrapper" title="io.TextIOWrapper"><code>io.TextIOWrapper</code></a> instance with the specified encoding, error handling behavior, and line ending(s).</p> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.3.</span></p> </div> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.4: </span>The <code>'x'</code> (exclusive creation) mode was added.</p> </div> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.6: </span>Accepts a <a class="reference internal" href="../glossary#term-path-like-object"><span class="xref std std-term">path-like object</span></a>.</p> </div> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="bz2.BZ2File">
<code>class bz2.BZ2File(filename, mode='r', *, compresslevel=9)</code> </dt> <dd>
<p>Open a bzip2-compressed file in binary mode.</p> <p>If <em>filename</em> is a <a class="reference internal" href="stdtypes#str" title="str"><code>str</code></a> or <a class="reference internal" href="stdtypes#bytes" title="bytes"><code>bytes</code></a> object, open the named file directly. Otherwise, <em>filename</em> should be a <a class="reference internal" href="../glossary#term-file-object"><span class="xref std std-term">file object</span></a>, which will be used to read or write the compressed data.</p> <p>The <em>mode</em> argument can be either <code>'r'</code> for reading (default), <code>'w'</code> for overwriting, <code>'x'</code> for exclusive creation, or <code>'a'</code> for appending. These can equivalently be given as <code>'rb'</code>, <code>'wb'</code>, <code>'xb'</code> and <code>'ab'</code> respectively.</p> <p>If <em>filename</em> is a file object (rather than an actual file name), a mode of <code>'w'</code> does not truncate the file, and is instead equivalent to <code>'a'</code>.</p> <p>If <em>mode</em> is <code>'w'</code> or <code>'a'</code>, <em>compresslevel</em> can be an integer between <code>1</code> and <code>9</code> specifying the level of compression: <code>1</code> produces the least compression, and <code>9</code> (default) produces the most compression.</p> <p>If <em>mode</em> is <code>'r'</code>, the input file may be the concatenation of multiple compressed streams.</p> <p><a class="reference internal" href="#bz2.BZ2File" title="bz2.BZ2File"><code>BZ2File</code></a> provides all of the members specified by the <a class="reference internal" href="io#io.BufferedIOBase" title="io.BufferedIOBase"><code>io.BufferedIOBase</code></a>, except for <a class="reference internal" href="io#io.BufferedIOBase.detach" title="io.BufferedIOBase.detach"><code>detach()</code></a> and <a class="reference internal" href="io#io.IOBase.truncate" title="io.IOBase.truncate"><code>truncate()</code></a>. Iteration and the <a class="reference internal" href="../reference/compound_stmts#with"><code>with</code></a> statement are supported.</p> <p><a class="reference internal" href="#bz2.BZ2File" title="bz2.BZ2File"><code>BZ2File</code></a> also provides the following methods:</p> <dl class="py method"> <dt class="sig sig-object py" id="bz2.BZ2File.peek">
<code>peek([n])</code> </dt> <dd>
<p>Return buffered data without advancing the file position. At least one byte of data will be returned (unless at EOF). The exact number of bytes returned is unspecified.</p> <div class="admonition note"> <p class="admonition-title">Note</p> <p>While calling <a class="reference internal" href="#bz2.BZ2File.peek" title="bz2.BZ2File.peek"><code>peek()</code></a> does not change the file position of the <a class="reference internal" href="#bz2.BZ2File" title="bz2.BZ2File"><code>BZ2File</code></a>, it may change the position of the underlying file object (e.g. if the <a class="reference internal" href="#bz2.BZ2File" title="bz2.BZ2File"><code>BZ2File</code></a> was constructed by passing a file object for <em>filename</em>).</p> </div> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.3.</span></p> </div> </dd>
</dl> <dl class="py method"> <dt class="sig sig-object py" id="bz2.BZ2File.fileno">
<code>fileno()</code> </dt> <dd>
<p>Return the file descriptor for the underlying file.</p> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.3.</span></p> </div> </dd>
</dl> <dl class="py method"> <dt class="sig sig-object py" id="bz2.BZ2File.readable">
<code>readable()</code> </dt> <dd>
<p>Return whether the file was opened for reading.</p> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.3.</span></p> </div> </dd>
</dl> <dl class="py method"> <dt class="sig sig-object py" id="bz2.BZ2File.seekable">
<code>seekable()</code> </dt> <dd>
<p>Return whether the file supports seeking.</p> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.3.</span></p> </div> </dd>
</dl> <dl class="py method"> <dt class="sig sig-object py" id="bz2.BZ2File.writable">
<code>writable()</code> </dt> <dd>
<p>Return whether the file was opened for writing.</p> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.3.</span></p> </div> </dd>
</dl> <dl class="py method"> <dt class="sig sig-object py" id="bz2.BZ2File.read1">
<code>read1(size=- 1)</code> </dt> <dd>
<p>Read up to <em>size</em> uncompressed bytes, while trying to avoid making multiple reads from the underlying stream. Reads up to a buffer’s worth of data if size is negative.</p> <p>Returns <code>b''</code> if the file is at EOF.</p> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.3.</span></p> </div> </dd>
</dl> <dl class="py method"> <dt class="sig sig-object py" id="bz2.BZ2File.readinto">
<code>readinto(b)</code> </dt> <dd>
<p>Read bytes into <em>b</em>.</p> <p>Returns the number of bytes read (0 for EOF).</p> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.3.</span></p> </div> </dd>
</dl> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.1: </span>Support for the <a class="reference internal" href="../reference/compound_stmts#with"><code>with</code></a> statement was added.</p> </div> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.3: </span>Support was added for <em>filename</em> being a <a class="reference internal" href="../glossary#term-file-object"><span class="xref std std-term">file object</span></a> instead of an actual filename.</p> </div> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.3: </span>The <code>'a'</code> (append) mode was added, along with support for reading multi-stream files.</p> </div> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.4: </span>The <code>'x'</code> (exclusive creation) mode was added.</p> </div> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.5: </span>The <a class="reference internal" href="io#io.BufferedIOBase.read" title="io.BufferedIOBase.read"><code>read()</code></a> method now accepts an argument of <code>None</code>.</p> </div> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.6: </span>Accepts a <a class="reference internal" href="../glossary#term-path-like-object"><span class="xref std std-term">path-like object</span></a>.</p> </div> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.9: </span>The <em>buffering</em> parameter has been removed. It was ignored and deprecated since Python 3.0. Pass an open file object to control how the file is opened.</p> <p>The <em>compresslevel</em> parameter became keyword-only.</p> </div> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.10: </span>This class is thread unsafe in the face of multiple simultaneous readers or writers, just like its equivalent classes in <a class="reference internal" href="gzip#module-gzip" title="gzip: Interfaces for gzip compression and decompression using file objects."><code>gzip</code></a> and <a class="reference internal" href="lzma#module-lzma" title="lzma: A Python wrapper for the liblzma compression library."><code>lzma</code></a> have always been.</p> </div> </dd>
</dl> </section> <section id="incremental-de-compression"> <h2>Incremental (de)compression</h2> <dl class="py class"> <dt class="sig sig-object py" id="bz2.BZ2Compressor">
<code>class bz2.BZ2Compressor(compresslevel=9)</code> </dt> <dd>
<p>Create a new compressor object. This object may be used to compress data incrementally. For one-shot compression, use the <a class="reference internal" href="#bz2.compress" title="bz2.compress"><code>compress()</code></a> function instead.</p> <p><em>compresslevel</em>, if given, must be an integer between <code>1</code> and <code>9</code>. The default is <code>9</code>.</p> <dl class="py method"> <dt class="sig sig-object py" id="bz2.BZ2Compressor.compress">
<code>compress(data)</code> </dt> <dd>
<p>Provide data to the compressor object. Returns a chunk of compressed data if possible, or an empty byte string otherwise.</p> <p>When you have finished providing data to the compressor, call the <a class="reference internal" href="#bz2.BZ2Compressor.flush" title="bz2.BZ2Compressor.flush"><code>flush()</code></a> method to finish the compression process.</p> </dd>
</dl> <dl class="py method"> <dt class="sig sig-object py" id="bz2.BZ2Compressor.flush">
<code>flush()</code> </dt> <dd>
<p>Finish the compression process. Returns the compressed data left in internal buffers.</p> <p>The compressor object may not be used after this method has been called.</p> </dd>
</dl> </dd>
</dl> <dl class="py class"> <dt class="sig sig-object py" id="bz2.BZ2Decompressor">
<code>class bz2.BZ2Decompressor</code> </dt> <dd>
<p>Create a new decompressor object. This object may be used to decompress data incrementally. For one-shot compression, use the <a class="reference internal" href="#bz2.decompress" title="bz2.decompress"><code>decompress()</code></a> function instead.</p> <div class="admonition note"> <p class="admonition-title">Note</p> <p>This class does not transparently handle inputs containing multiple compressed streams, unlike <a class="reference internal" href="#bz2.decompress" title="bz2.decompress"><code>decompress()</code></a> and <a class="reference internal" href="#bz2.BZ2File" title="bz2.BZ2File"><code>BZ2File</code></a>. If you need to decompress a multi-stream input with <a class="reference internal" href="#bz2.BZ2Decompressor" title="bz2.BZ2Decompressor"><code>BZ2Decompressor</code></a>, you must use a new decompressor for each stream.</p> </div> <dl class="py method"> <dt class="sig sig-object py" id="bz2.BZ2Decompressor.decompress">
<code>decompress(data, max_length=- 1)</code> </dt> <dd>
<p>Decompress <em>data</em> (a <a class="reference internal" href="../glossary#term-bytes-like-object"><span class="xref std std-term">bytes-like object</span></a>), returning uncompressed data as bytes. Some of <em>data</em> may be buffered internally, for use in later calls to <a class="reference internal" href="#bz2.decompress" title="bz2.decompress"><code>decompress()</code></a>. The returned data should be concatenated with the output of any previous calls to <a class="reference internal" href="#bz2.decompress" title="bz2.decompress"><code>decompress()</code></a>.</p> <p>If <em>max_length</em> is nonnegative, returns at most <em>max_length</em> bytes of decompressed data. If this limit is reached and further output can be produced, the <a class="reference internal" href="#bz2.BZ2Decompressor.needs_input" title="bz2.BZ2Decompressor.needs_input"><code>needs_input</code></a> attribute will be set to <code>False</code>. In this case, the next call to <a class="reference internal" href="#bz2.BZ2Decompressor.decompress" title="bz2.BZ2Decompressor.decompress"><code>decompress()</code></a> may provide <em>data</em> as <code>b''</code> to obtain more of the output.</p> <p>If all of the input data was decompressed and returned (either because this was less than <em>max_length</em> bytes, or because <em>max_length</em> was negative), the <a class="reference internal" href="#bz2.BZ2Decompressor.needs_input" title="bz2.BZ2Decompressor.needs_input"><code>needs_input</code></a> attribute will be set to <code>True</code>.</p> <p>Attempting to decompress data after the end of stream is reached raises an <a class="reference internal" href="exceptions#EOFError" title="EOFError"><code>EOFError</code></a>. Any data found after the end of the stream is ignored and saved in the <a class="reference internal" href="#bz2.BZ2Decompressor.unused_data" title="bz2.BZ2Decompressor.unused_data"><code>unused_data</code></a> attribute.</p> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.5: </span>Added the <em>max_length</em> parameter.</p> </div> </dd>
</dl> <dl class="py attribute"> <dt class="sig sig-object py" id="bz2.BZ2Decompressor.eof">
<code>eof</code> </dt> <dd>
<p><code>True</code> if the end-of-stream marker has been reached.</p> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.3.</span></p> </div> </dd>
</dl> <dl class="py attribute"> <dt class="sig sig-object py" id="bz2.BZ2Decompressor.unused_data">
<code>unused_data</code> </dt> <dd>
<p>Data found after the end of the compressed stream.</p> <p>If this attribute is accessed before the end of the stream has been reached, its value will be <code>b''</code>.</p> </dd>
</dl> <dl class="py attribute"> <dt class="sig sig-object py" id="bz2.BZ2Decompressor.needs_input">
<code>needs_input</code> </dt> <dd>
<p><code>False</code> if the <a class="reference internal" href="#bz2.BZ2Decompressor.decompress" title="bz2.BZ2Decompressor.decompress"><code>decompress()</code></a> method can provide more decompressed data before requiring new uncompressed input.</p> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.5.</span></p> </div> </dd>
</dl> </dd>
</dl> </section> <section id="one-shot-de-compression"> <h2>One-shot (de)compression</h2> <dl class="py function"> <dt class="sig sig-object py" id="bz2.compress">
<code>bz2.compress(data, compresslevel=9)</code> </dt> <dd>
<p>Compress <em>data</em>, a <a class="reference internal" href="../glossary#term-bytes-like-object"><span class="xref std std-term">bytes-like object</span></a>.</p> <p><em>compresslevel</em>, if given, must be an integer between <code>1</code> and <code>9</code>. The default is <code>9</code>.</p> <p>For incremental compression, use a <a class="reference internal" href="#bz2.BZ2Compressor" title="bz2.BZ2Compressor"><code>BZ2Compressor</code></a> instead.</p> </dd>
</dl> <dl class="py function"> <dt class="sig sig-object py" id="bz2.decompress">
<code>bz2.decompress(data)</code> </dt> <dd>
<p>Decompress <em>data</em>, a <a class="reference internal" href="../glossary#term-bytes-like-object"><span class="xref std std-term">bytes-like object</span></a>.</p> <p>If <em>data</em> is the concatenation of multiple compressed streams, decompress all of the streams.</p> <p>For incremental decompression, use a <a class="reference internal" href="#bz2.BZ2Decompressor" title="bz2.BZ2Decompressor"><code>BZ2Decompressor</code></a> instead.</p> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.3: </span>Support for multi-stream inputs was added.</p> </div> </dd>
</dl> </section> <section id="examples-of-usage"> <span id="bz2-usage-examples"></span><h2>Examples of usage</h2> <p>Below are some examples of typical usage of the <a class="reference internal" href="#module-bz2" title="bz2: Interfaces for bzip2 compression and decompression."><code>bz2</code></a> module.</p> <p>Using <a class="reference internal" href="#bz2.compress" title="bz2.compress"><code>compress()</code></a> and <a class="reference internal" href="#bz2.decompress" title="bz2.decompress"><code>decompress()</code></a> to demonstrate round-trip compression:</p> <pre data-language="python">>>> import bz2
>>> data = b"""\
... Donec rhoncus quis sapien sit amet molestie. Fusce scelerisque vel augue
... nec ullamcorper. Nam rutrum pretium placerat. Aliquam vel tristique lorem,
... sit amet cursus ante. In interdum laoreet mi, sit amet ultrices purus
... pulvinar a. Nam gravida euismod magna, non varius justo tincidunt feugiat.
... Aliquam pharetra lacus non risus vehicula rutrum. Maecenas aliquam leo
... felis. Pellentesque semper nunc sit amet nibh ullamcorper, ac elementum
... dolor luctus. Curabitur lacinia mi ornare consectetur vestibulum."""
>>> c = bz2.compress(data)
>>> len(data) / len(c) # Data compression ratio
1.513595166163142
>>> d = bz2.decompress(c)
>>> data == d # Check equality to original object after round-trip
True
</pre> <p>Using <a class="reference internal" href="#bz2.BZ2Compressor" title="bz2.BZ2Compressor"><code>BZ2Compressor</code></a> for incremental compression:</p> <pre data-language="python">>>> import bz2
>>> def gen_data(chunks=10, chunksize=1000):
... """Yield incremental blocks of chunksize bytes."""
... for _ in range(chunks):
... yield b"z" * chunksize
...
>>> comp = bz2.BZ2Compressor()
>>> out = b""
>>> for chunk in gen_data():
... # Provide data to the compressor object
... out = out + comp.compress(chunk)
...
>>> # Finish the compression process. Call this once you have
>>> # finished providing data to the compressor.
>>> out = out + comp.flush()
</pre> <p>The example above uses a very “nonrandom” stream of data (a stream of <code>b"z"</code> chunks). Random data tends to compress poorly, while ordered, repetitive data usually yields a high compression ratio.</p> <p>Writing and reading a bzip2-compressed file in binary mode:</p> <pre data-language="python">>>> import bz2
>>> data = b"""\
... Donec rhoncus quis sapien sit amet molestie. Fusce scelerisque vel augue
... nec ullamcorper. Nam rutrum pretium placerat. Aliquam vel tristique lorem,
... sit amet cursus ante. In interdum laoreet mi, sit amet ultrices purus
... pulvinar a. Nam gravida euismod magna, non varius justo tincidunt feugiat.
... Aliquam pharetra lacus non risus vehicula rutrum. Maecenas aliquam leo
... felis. Pellentesque semper nunc sit amet nibh ullamcorper, ac elementum
... dolor luctus. Curabitur lacinia mi ornare consectetur vestibulum."""
>>> with bz2.open("myfile.bz2", "wb") as f:
... # Write compressed data to file
... unused = f.write(data)
...
>>> with bz2.open("myfile.bz2", "rb") as f:
... # Decompress data from file
... content = f.read()
...
>>> content == data # Check equality to original object after round-trip
True
</pre> </section> <div class="_attribution">
<p class="_attribution-p">
© 2001–2023 Python Software Foundation<br>Licensed under the PSF License.<br>
<a href="https://docs.python.org/3.12/library/bz2.html" class="_attribution-link">https://docs.python.org/3.12/library/bz2.html</a>
</p>
</div>
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