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<div class="section" id="module-bz2">
<span id="bz2-support-for-bzip2-compression"></span><h1><a class="reference internal" href="#module-bz2" title="bz2: Interfaces for bzip2 compression and decompression."><code class="xref py py-mod docutils literal notranslate"><span class="pre">bz2</span></code></a> — Support for <strong class="program">bzip2</strong> compression<a class="headerlink" href="#module-bz2" title="Permalink to this headline">¶</a></h1>
<p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.7/Lib/bz2.py">Lib/bz2.py</a></p>
<hr class="docutils" />
<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 class="xref py py-mod docutils literal notranslate"><span class="pre">bz2</span></code></a> module contains:</p>
<ul class="simple">
<li><p>The <a class="reference internal" href="#bz2.open" title="bz2.open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a> function and <a class="reference internal" href="#bz2.BZ2File" title="bz2.BZ2File"><code class="xref py py-class docutils literal notranslate"><span class="pre">BZ2File</span></code></a> class for reading and
writing compressed files.</p></li>
<li><p>The <a class="reference internal" href="#bz2.BZ2Compressor" title="bz2.BZ2Compressor"><code class="xref py py-class docutils literal notranslate"><span class="pre">BZ2Compressor</span></code></a> and <a class="reference internal" href="#bz2.BZ2Decompressor" title="bz2.BZ2Decompressor"><code class="xref py py-class docutils literal notranslate"><span class="pre">BZ2Decompressor</span></code></a> classes for
incremental (de)compression.</p></li>
<li><p>The <a class="reference internal" href="#bz2.compress" title="bz2.compress"><code class="xref py py-func docutils literal notranslate"><span class="pre">compress()</span></code></a> and <a class="reference internal" href="#bz2.decompress" title="bz2.decompress"><code class="xref py py-func docutils literal notranslate"><span class="pre">decompress()</span></code></a> functions for one-shot
(de)compression.</p></li>
</ul>
<p>All of the classes in this module may safely be accessed from multiple threads.</p>
<div class="section" id="de-compression-of-files">
<h2>(De)compression of files<a class="headerlink" href="#de-compression-of-files" title="Permalink to this headline">¶</a></h2>
<dl class="function">
<dt id="bz2.open">
<code class="sig-prename descclassname">bz2.</code><code class="sig-name descname">open</code><span class="sig-paren">(</span><em class="sig-param">filename</em>, <em class="sig-param">mode='r'</em>, <em class="sig-param">compresslevel=9</em>, <em class="sig-param">encoding=None</em>, <em class="sig-param">errors=None</em>, <em class="sig-param">newline=None</em><span class="sig-paren">)</span><a class="headerlink" href="#bz2.open" title="Permalink to this definition">¶</a></dt>
<dd><p>Open a bzip2-compressed file in binary or text mode, returning a <a class="reference internal" href="../glossary.html#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 class="xref py py-class docutils literal notranslate"><span class="pre">BZ2File</span></code></a>, the <em>filename</em> argument can be
an actual filename (a <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> or <a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></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 class="docutils literal notranslate"><span class="pre">'r'</span></code>, <code class="docutils literal notranslate"><span class="pre">'rb'</span></code>, <code class="docutils literal notranslate"><span class="pre">'w'</span></code>, <code class="docutils literal notranslate"><span class="pre">'wb'</span></code>,
<code class="docutils literal notranslate"><span class="pre">'x'</span></code>, <code class="docutils literal notranslate"><span class="pre">'xb'</span></code>, <code class="docutils literal notranslate"><span class="pre">'a'</span></code> or <code class="docutils literal notranslate"><span class="pre">'ab'</span></code> for binary mode, or <code class="docutils literal notranslate"><span class="pre">'rt'</span></code>,
<code class="docutils literal notranslate"><span class="pre">'wt'</span></code>, <code class="docutils literal notranslate"><span class="pre">'xt'</span></code>, or <code class="docutils literal notranslate"><span class="pre">'at'</span></code> for text mode. The default is <code class="docutils literal notranslate"><span class="pre">'rb'</span></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 class="xref py py-class docutils literal notranslate"><span class="pre">BZ2File</span></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 class="xref py py-class docutils literal notranslate"><span class="pre">BZ2File</span></code></a>
constructor: <code class="docutils literal notranslate"><span class="pre">BZ2File(filename,</span> <span class="pre">mode,</span> <span class="pre">compresslevel=compresslevel)</span></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 class="xref py py-class docutils literal notranslate"><span class="pre">BZ2File</span></code></a> object is created, and wrapped in an
<a class="reference internal" href="io.html#io.TextIOWrapper" title="io.TextIOWrapper"><code class="xref py py-class docutils literal notranslate"><span class="pre">io.TextIOWrapper</span></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 class="docutils literal notranslate"><span class="pre">'x'</span></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.html#term-path-like-object"><span class="xref std std-term">path-like object</span></a>.</p>
</div>
</dd></dl>
<dl class="class">
<dt id="bz2.BZ2File">
<em class="property">class </em><code class="sig-prename descclassname">bz2.</code><code class="sig-name descname">BZ2File</code><span class="sig-paren">(</span><em class="sig-param">filename</em>, <em class="sig-param">mode='r'</em>, <em class="sig-param">buffering=None</em>, <em class="sig-param">compresslevel=9</em><span class="sig-paren">)</span><a class="headerlink" href="#bz2.BZ2File" title="Permalink to this definition">¶</a></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.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> or <a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> object, open the named file
directly. Otherwise, <em>filename</em> should be a <a class="reference internal" href="../glossary.html#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 class="docutils literal notranslate"><span class="pre">'r'</span></code> for reading (default), <code class="docutils literal notranslate"><span class="pre">'w'</span></code> for
overwriting, <code class="docutils literal notranslate"><span class="pre">'x'</span></code> for exclusive creation, or <code class="docutils literal notranslate"><span class="pre">'a'</span></code> for appending. These
can equivalently be given as <code class="docutils literal notranslate"><span class="pre">'rb'</span></code>, <code class="docutils literal notranslate"><span class="pre">'wb'</span></code>, <code class="docutils literal notranslate"><span class="pre">'xb'</span></code> and <code class="docutils literal notranslate"><span class="pre">'ab'</span></code>
respectively.</p>
<p>If <em>filename</em> is a file object (rather than an actual file name), a mode of
<code class="docutils literal notranslate"><span class="pre">'w'</span></code> does not truncate the file, and is instead equivalent to <code class="docutils literal notranslate"><span class="pre">'a'</span></code>.</p>
<p>The <em>buffering</em> argument is ignored. Its use is deprecated.</p>
<p>If <em>mode</em> is <code class="docutils literal notranslate"><span class="pre">'w'</span></code> or <code class="docutils literal notranslate"><span class="pre">'a'</span></code>, <em>compresslevel</em> can be an integer between
<code class="docutils literal notranslate"><span class="pre">1</span></code> and <code class="docutils literal notranslate"><span class="pre">9</span></code> specifying the level of compression: <code class="docutils literal notranslate"><span class="pre">1</span></code> produces the
least compression, and <code class="docutils literal notranslate"><span class="pre">9</span></code> (default) produces the most compression.</p>
<p>If <em>mode</em> is <code class="docutils literal notranslate"><span class="pre">'r'</span></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 class="xref py py-class docutils literal notranslate"><span class="pre">BZ2File</span></code></a> provides all of the members specified by the
<a class="reference internal" href="io.html#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">io.BufferedIOBase</span></code></a>, except for <code class="xref py py-meth docutils literal notranslate"><span class="pre">detach()</span></code> and <code class="xref py py-meth docutils literal notranslate"><span class="pre">truncate()</span></code>.
Iteration and the <a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code></a> statement are supported.</p>
<p><a class="reference internal" href="#bz2.BZ2File" title="bz2.BZ2File"><code class="xref py py-class docutils literal notranslate"><span class="pre">BZ2File</span></code></a> also provides the following method:</p>
<dl class="method">
<dt id="bz2.BZ2File.peek">
<code class="sig-name descname">peek</code><span class="sig-paren">(</span><span class="optional">[</span><em class="sig-param">n</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#bz2.BZ2File.peek" title="Permalink to this definition">¶</a></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 class="xref py py-meth docutils literal notranslate"><span class="pre">peek()</span></code></a> does not change the file position of
the <a class="reference internal" href="#bz2.BZ2File" title="bz2.BZ2File"><code class="xref py py-class docutils literal notranslate"><span class="pre">BZ2File</span></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 class="xref py py-class docutils literal notranslate"><span class="pre">BZ2File</span></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>
<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.html#with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code></a> statement was added.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.3: </span>The <code class="xref py py-meth docutils literal notranslate"><span class="pre">fileno()</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">readable()</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">seekable()</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">writable()</span></code>,
<code class="xref py py-meth docutils literal notranslate"><span class="pre">read1()</span></code> and <code class="xref py py-meth docutils literal notranslate"><span class="pre">readinto()</span></code> methods were 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.html#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 class="docutils literal notranslate"><span class="pre">'a'</span></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 class="docutils literal notranslate"><span class="pre">'x'</span></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.html#io.BufferedIOBase.read" title="io.BufferedIOBase.read"><code class="xref py py-meth docutils literal notranslate"><span class="pre">read()</span></code></a> method now accepts an argument of
<code class="docutils literal notranslate"><span class="pre">None</span></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.html#term-path-like-object"><span class="xref std std-term">path-like object</span></a>.</p>
</div>
</dd></dl>
</div>
<div class="section" id="incremental-de-compression">
<h2>Incremental (de)compression<a class="headerlink" href="#incremental-de-compression" title="Permalink to this headline">¶</a></h2>
<dl class="class">
<dt id="bz2.BZ2Compressor">
<em class="property">class </em><code class="sig-prename descclassname">bz2.</code><code class="sig-name descname">BZ2Compressor</code><span class="sig-paren">(</span><em class="sig-param">compresslevel=9</em><span class="sig-paren">)</span><a class="headerlink" href="#bz2.BZ2Compressor" title="Permalink to this definition">¶</a></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 class="xref py py-func docutils literal notranslate"><span class="pre">compress()</span></code></a> function
instead.</p>
<p><em>compresslevel</em>, if given, must be an integer between <code class="docutils literal notranslate"><span class="pre">1</span></code> and <code class="docutils literal notranslate"><span class="pre">9</span></code>. The
default is <code class="docutils literal notranslate"><span class="pre">9</span></code>.</p>
<dl class="method">
<dt id="bz2.BZ2Compressor.compress">
<code class="sig-name descname">compress</code><span class="sig-paren">(</span><em class="sig-param">data</em><span class="sig-paren">)</span><a class="headerlink" href="#bz2.BZ2Compressor.compress" title="Permalink to this definition">¶</a></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 class="xref py py-meth docutils literal notranslate"><span class="pre">flush()</span></code></a> method to finish the compression process.</p>
</dd></dl>
<dl class="method">
<dt id="bz2.BZ2Compressor.flush">
<code class="sig-name descname">flush</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#bz2.BZ2Compressor.flush" title="Permalink to this definition">¶</a></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="class">
<dt id="bz2.BZ2Decompressor">
<em class="property">class </em><code class="sig-prename descclassname">bz2.</code><code class="sig-name descname">BZ2Decompressor</code><a class="headerlink" href="#bz2.BZ2Decompressor" title="Permalink to this definition">¶</a></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 class="xref py py-func docutils literal notranslate"><span class="pre">decompress()</span></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 class="xref py py-func docutils literal notranslate"><span class="pre">decompress()</span></code></a> and <a class="reference internal" href="#bz2.BZ2File" title="bz2.BZ2File"><code class="xref py py-class docutils literal notranslate"><span class="pre">BZ2File</span></code></a>. If
you need to decompress a multi-stream input with <a class="reference internal" href="#bz2.BZ2Decompressor" title="bz2.BZ2Decompressor"><code class="xref py py-class docutils literal notranslate"><span class="pre">BZ2Decompressor</span></code></a>,
you must use a new decompressor for each stream.</p>
</div>
<dl class="method">
<dt id="bz2.BZ2Decompressor.decompress">
<code class="sig-name descname">decompress</code><span class="sig-paren">(</span><em class="sig-param">data</em>, <em class="sig-param">max_length=-1</em><span class="sig-paren">)</span><a class="headerlink" href="#bz2.BZ2Decompressor.decompress" title="Permalink to this definition">¶</a></dt>
<dd><p>Decompress <em>data</em> (a <a class="reference internal" href="../glossary.html#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 class="xref py py-meth docutils literal notranslate"><span class="pre">decompress()</span></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 class="xref py py-meth docutils literal notranslate"><span class="pre">decompress()</span></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 class="xref py py-attr docutils literal notranslate"><span class="pre">needs_input</span></code></a> attribute will
be set to <code class="docutils literal notranslate"><span class="pre">False</span></code>. In this case, the next call to
<a class="reference internal" href="#bz2.BZ2Decompressor.decompress" title="bz2.BZ2Decompressor.decompress"><code class="xref py py-meth docutils literal notranslate"><span class="pre">decompress()</span></code></a> may provide <em>data</em> as <code class="docutils literal notranslate"><span class="pre">b''</span></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 class="xref py py-attr docutils literal notranslate"><span class="pre">needs_input</span></code></a> attribute
will be set to <code class="docutils literal notranslate"><span class="pre">True</span></code>.</p>
<p>Attempting to decompress data after the end of stream is reached
raises an <cite>EOFError</cite>. 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 class="xref py py-attr docutils literal notranslate"><span class="pre">unused_data</span></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="attribute">
<dt id="bz2.BZ2Decompressor.eof">
<code class="sig-name descname">eof</code><a class="headerlink" href="#bz2.BZ2Decompressor.eof" title="Permalink to this definition">¶</a></dt>
<dd><p><code class="docutils literal notranslate"><span class="pre">True</span></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="attribute">
<dt id="bz2.BZ2Decompressor.unused_data">
<code class="sig-name descname">unused_data</code><a class="headerlink" href="#bz2.BZ2Decompressor.unused_data" title="Permalink to this definition">¶</a></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 class="docutils literal notranslate"><span class="pre">b''</span></code>.</p>
</dd></dl>
<dl class="attribute">
<dt id="bz2.BZ2Decompressor.needs_input">
<code class="sig-name descname">needs_input</code><a class="headerlink" href="#bz2.BZ2Decompressor.needs_input" title="Permalink to this definition">¶</a></dt>
<dd><p><code class="docutils literal notranslate"><span class="pre">False</span></code> if the <a class="reference internal" href="#bz2.BZ2Decompressor.decompress" title="bz2.BZ2Decompressor.decompress"><code class="xref py py-meth docutils literal notranslate"><span class="pre">decompress()</span></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>
</div>
<div class="section" id="one-shot-de-compression">
<h2>One-shot (de)compression<a class="headerlink" href="#one-shot-de-compression" title="Permalink to this headline">¶</a></h2>
<dl class="function">
<dt id="bz2.compress">
<code class="sig-prename descclassname">bz2.</code><code class="sig-name descname">compress</code><span class="sig-paren">(</span><em class="sig-param">data</em>, <em class="sig-param">compresslevel=9</em><span class="sig-paren">)</span><a class="headerlink" href="#bz2.compress" title="Permalink to this definition">¶</a></dt>
<dd><p>Compress <em>data</em>, a <a class="reference internal" href="../glossary.html#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 class="docutils literal notranslate"><span class="pre">1</span></code> and <code class="docutils literal notranslate"><span class="pre">9</span></code>. The
default is <code class="docutils literal notranslate"><span class="pre">9</span></code>.</p>
<p>For incremental compression, use a <a class="reference internal" href="#bz2.BZ2Compressor" title="bz2.BZ2Compressor"><code class="xref py py-class docutils literal notranslate"><span class="pre">BZ2Compressor</span></code></a> instead.</p>
</dd></dl>
<dl class="function">
<dt id="bz2.decompress">
<code class="sig-prename descclassname">bz2.</code><code class="sig-name descname">decompress</code><span class="sig-paren">(</span><em class="sig-param">data</em><span class="sig-paren">)</span><a class="headerlink" href="#bz2.decompress" title="Permalink to this definition">¶</a></dt>
<dd><p>Decompress <em>data</em>, a <a class="reference internal" href="../glossary.html#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 class="xref py py-class docutils literal notranslate"><span class="pre">BZ2Decompressor</span></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>
</div>
<div class="section" id="examples-of-usage">
<span id="bz2-usage-examples"></span><h2>Examples of usage<a class="headerlink" href="#examples-of-usage" title="Permalink to this headline">¶</a></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 class="xref py py-mod docutils literal notranslate"><span class="pre">bz2</span></code></a> module.</p>
<p>Using <a class="reference internal" href="#bz2.compress" title="bz2.compress"><code class="xref py py-func docutils literal notranslate"><span class="pre">compress()</span></code></a> and <a class="reference internal" href="#bz2.decompress" title="bz2.decompress"><code class="xref py py-func docutils literal notranslate"><span class="pre">decompress()</span></code></a> to demonstrate round-trip compression:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">bz2</span>
</pre></div>
</div>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">data</span> <span class="o">=</span> <span class="sa">b</span><span class="s2">"""</span><span class="se">\</span>
<span class="gp">... </span><span class="s2">Donec rhoncus quis sapien sit amet molestie. Fusce scelerisque vel augue</span>
<span class="gp">... </span><span class="s2">nec ullamcorper. Nam rutrum pretium placerat. Aliquam vel tristique lorem,</span>
<span class="gp">... </span><span class="s2">sit amet cursus ante. In interdum laoreet mi, sit amet ultrices purus</span>
<span class="gp">... </span><span class="s2">pulvinar a. Nam gravida euismod magna, non varius justo tincidunt feugiat.</span>
<span class="gp">... </span><span class="s2">Aliquam pharetra lacus non risus vehicula rutrum. Maecenas aliquam leo</span>
<span class="gp">... </span><span class="s2">felis. Pellentesque semper nunc sit amet nibh ullamcorper, ac elementum</span>
<span class="gp">... </span><span class="s2">dolor luctus. Curabitur lacinia mi ornare consectetur vestibulum."""</span>
</pre></div>
</div>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">c</span> <span class="o">=</span> <span class="n">bz2</span><span class="o">.</span><span class="n">compress</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">len</span><span class="p">(</span><span class="n">data</span><span class="p">)</span> <span class="o">/</span> <span class="nb">len</span><span class="p">(</span><span class="n">c</span><span class="p">)</span> <span class="c1"># Data compression ratio</span>
<span class="go">1.513595166163142</span>
</pre></div>
</div>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">d</span> <span class="o">=</span> <span class="n">bz2</span><span class="o">.</span><span class="n">decompress</span><span class="p">(</span><span class="n">c</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">data</span> <span class="o">==</span> <span class="n">d</span> <span class="c1"># Check equality to original object after round-trip</span>
<span class="go">True</span>
</pre></div>
</div>
<p>Using <a class="reference internal" href="#bz2.BZ2Compressor" title="bz2.BZ2Compressor"><code class="xref py py-class docutils literal notranslate"><span class="pre">BZ2Compressor</span></code></a> for incremental compression:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">bz2</span>
</pre></div>
</div>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">def</span> <span class="nf">gen_data</span><span class="p">(</span><span class="n">chunks</span><span class="o">=</span><span class="mi">10</span><span class="p">,</span> <span class="n">chunksize</span><span class="o">=</span><span class="mi">1000</span><span class="p">):</span>
<span class="gp">... </span> <span class="sd">"""Yield incremental blocks of chunksize bytes."""</span>
<span class="gp">... </span> <span class="k">for</span> <span class="n">_</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="n">chunks</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">yield</span> <span class="sa">b</span><span class="s2">"z"</span> <span class="o">*</span> <span class="n">chunksize</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="n">comp</span> <span class="o">=</span> <span class="n">bz2</span><span class="o">.</span><span class="n">BZ2Compressor</span><span class="p">()</span>
<span class="gp">>>> </span><span class="n">out</span> <span class="o">=</span> <span class="sa">b</span><span class="s2">""</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">chunk</span> <span class="ow">in</span> <span class="n">gen_data</span><span class="p">():</span>
<span class="gp">... </span> <span class="c1"># Provide data to the compressor object</span>
<span class="gp">... </span> <span class="n">out</span> <span class="o">=</span> <span class="n">out</span> <span class="o">+</span> <span class="n">comp</span><span class="o">.</span><span class="n">compress</span><span class="p">(</span><span class="n">chunk</span><span class="p">)</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="c1"># Finish the compression process. Call this once you have</span>
<span class="gp">>>> </span><span class="c1"># finished providing data to the compressor.</span>
<span class="gp">>>> </span><span class="n">out</span> <span class="o">=</span> <span class="n">out</span> <span class="o">+</span> <span class="n">comp</span><span class="o">.</span><span class="n">flush</span><span class="p">()</span>
</pre></div>
</div>
<p>The example above uses a very “nonrandom” stream of data
(a stream of <cite>b”z”</cite> 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>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">bz2</span>
</pre></div>
</div>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">data</span> <span class="o">=</span> <span class="sa">b</span><span class="s2">"""</span><span class="se">\</span>
<span class="gp">... </span><span class="s2">Donec rhoncus quis sapien sit amet molestie. Fusce scelerisque vel augue</span>
<span class="gp">... </span><span class="s2">nec ullamcorper. Nam rutrum pretium placerat. Aliquam vel tristique lorem,</span>
<span class="gp">... </span><span class="s2">sit amet cursus ante. In interdum laoreet mi, sit amet ultrices purus</span>
<span class="gp">... </span><span class="s2">pulvinar a. Nam gravida euismod magna, non varius justo tincidunt feugiat.</span>
<span class="gp">... </span><span class="s2">Aliquam pharetra lacus non risus vehicula rutrum. Maecenas aliquam leo</span>
<span class="gp">... </span><span class="s2">felis. Pellentesque semper nunc sit amet nibh ullamcorper, ac elementum</span>
<span class="gp">... </span><span class="s2">dolor luctus. Curabitur lacinia mi ornare consectetur vestibulum."""</span>
</pre></div>
</div>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">with</span> <span class="n">bz2</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="s2">"myfile.bz2"</span><span class="p">,</span> <span class="s2">"wb"</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span>
<span class="gp">... </span> <span class="c1"># Write compressed data to file</span>
<span class="gp">... </span> <span class="n">unused</span> <span class="o">=</span> <span class="n">f</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>
</pre></div>
</div>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">with</span> <span class="n">bz2</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="s2">"myfile.bz2"</span><span class="p">,</span> <span class="s2">"rb"</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span>
<span class="gp">... </span> <span class="c1"># Decompress data from file</span>
<span class="gp">... </span> <span class="n">content</span> <span class="o">=</span> <span class="n">f</span><span class="o">.</span><span class="n">read</span><span class="p">()</span>
</pre></div>
</div>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">content</span> <span class="o">==</span> <span class="n">data</span> <span class="c1"># Check equality to original object after round-trip</span>
<span class="go">True</span>
</pre></div>
</div>
</div>
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<ul>
<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">bz2</span></code> — Support for <strong class="program">bzip2</strong> compression</a><ul>
<li><a class="reference internal" href="#de-compression-of-files">(De)compression of files</a></li>
<li><a class="reference internal" href="#incremental-de-compression">Incremental (de)compression</a></li>
<li><a class="reference internal" href="#one-shot-de-compression">One-shot (de)compression</a></li>
<li><a class="reference internal" href="#examples-of-usage">Examples of usage</a></li>
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<h4>Previous topic</h4>
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