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<div class="section" id="module-bz2">
<h1>13.3. <tt class="xref docutils literal"><span class="pre">bz2</span></tt> — Compression compatible with <strong>bzip2</strong><a class="headerlink" href="#module-bz2" title="Permalink to this headline">¶</a></h1>
<p class="versionadded">
<span class="versionmodified">New in version 2.3.</span></p>
<p>This module provides a comprehensive interface for the bz2 compression library.
It implements a complete file interface, one-shot (de)compression functions, and
types for sequential (de)compression.</p>
<p>For other archive formats, see the <a title="Interfaces for gzip compression and decompression using file objects." class="reference external" href="gzip.html#module-gzip"><tt class="xref docutils literal"><span class="pre">gzip</span></tt></a>, <a title="Read and write ZIP-format archive files." class="reference external" href="zipfile.html#module-zipfile"><tt class="xref docutils literal"><span class="pre">zipfile</span></tt></a>, and
<a title="Read and write tar-format archive files." class="reference external" href="tarfile.html#module-tarfile"><tt class="xref docutils literal"><span class="pre">tarfile</span></tt></a> modules.</p>
<p>Here is a summary of the features offered by the bz2 module:</p>
<ul class="simple">
<li><a title="bz2.BZ2File" class="reference internal" href="#bz2.BZ2File"><tt class="xref docutils literal"><span class="pre">BZ2File</span></tt></a> class implements a complete file interface, including
<tt class="xref docutils literal"><span class="pre">readline()</span></tt>, <tt class="xref docutils literal"><span class="pre">readlines()</span></tt>, <tt class="xref docutils literal"><span class="pre">writelines()</span></tt>, <tt class="xref docutils literal"><span class="pre">seek()</span></tt>, etc;</li>
<li><a title="bz2.BZ2File" class="reference internal" href="#bz2.BZ2File"><tt class="xref docutils literal"><span class="pre">BZ2File</span></tt></a> class implements emulated <tt class="xref docutils literal"><span class="pre">seek()</span></tt> support;</li>
<li><a title="bz2.BZ2File" class="reference internal" href="#bz2.BZ2File"><tt class="xref docutils literal"><span class="pre">BZ2File</span></tt></a> class implements universal newline support;</li>
<li><a title="bz2.BZ2File" class="reference internal" href="#bz2.BZ2File"><tt class="xref docutils literal"><span class="pre">BZ2File</span></tt></a> class offers an optimized line iteration using the readahead
algorithm borrowed from file objects;</li>
<li>Sequential (de)compression supported by <a title="bz2.BZ2Compressor" class="reference internal" href="#bz2.BZ2Compressor"><tt class="xref docutils literal"><span class="pre">BZ2Compressor</span></tt></a> and
<a title="bz2.BZ2Decompressor" class="reference internal" href="#bz2.BZ2Decompressor"><tt class="xref docutils literal"><span class="pre">BZ2Decompressor</span></tt></a> classes;</li>
<li>One-shot (de)compression supported by <a title="bz2.compress" class="reference internal" href="#bz2.compress"><tt class="xref docutils literal"><span class="pre">compress()</span></tt></a> and <a title="bz2.decompress" class="reference internal" href="#bz2.decompress"><tt class="xref docutils literal"><span class="pre">decompress()</span></tt></a>
functions;</li>
<li>Thread safety uses individual locking mechanism.</li>
</ul>
<div class="section" id="de-compression-of-files">
<h2>13.3.1. (De)compression of files<a class="headerlink" href="#de-compression-of-files" title="Permalink to this headline">¶</a></h2>
<p>Handling of compressed files is offered by the <a title="bz2.BZ2File" class="reference internal" href="#bz2.BZ2File"><tt class="xref docutils literal"><span class="pre">BZ2File</span></tt></a> class.</p>
<dl class="class">
<dt id="bz2.BZ2File">
<em class="property">class </em><tt class="descclassname">bz2.</tt><tt class="descname">BZ2File</tt><big>(</big><em>filename</em><span class="optional">[</span>, <em>mode</em><span class="optional">[</span>, <em>buffering</em><span class="optional">[</span>, <em>compresslevel</em><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><big>)</big><a class="headerlink" href="#bz2.BZ2File" title="Permalink to this definition">¶</a></dt>
<dd><p>Open a bz2 file. Mode can be either <tt class="docutils literal"><span class="pre">'r'</span></tt> or <tt class="docutils literal"><span class="pre">'w'</span></tt>, for reading (default)
or writing. When opened for writing, the file will be created if it doesn’t
exist, and truncated otherwise. If <em>buffering</em> is given, <tt class="docutils literal"><span class="pre">0</span></tt> means
unbuffered, and larger numbers specify the buffer size; the default is
<tt class="docutils literal"><span class="pre">0</span></tt>. If <em>compresslevel</em> is given, it must be a number between <tt class="docutils literal"><span class="pre">1</span></tt> and
<tt class="docutils literal"><span class="pre">9</span></tt>; the default is <tt class="docutils literal"><span class="pre">9</span></tt>. Add a <tt class="docutils literal"><span class="pre">'U'</span></tt> to mode to open the file for input
with universal newline support. Any line ending in the input file will be
seen as a <tt class="docutils literal"><span class="pre">'\n'</span></tt> in Python. Also, a file so opened gains the attribute
<tt class="xref docutils literal"><span class="pre">newlines</span></tt>; the value for this attribute is one of <tt class="xref docutils literal"><span class="pre">None</span></tt> (no newline
read yet), <tt class="docutils literal"><span class="pre">'\r'</span></tt>, <tt class="docutils literal"><span class="pre">'\n'</span></tt>, <tt class="docutils literal"><span class="pre">'\r\n'</span></tt> or a tuple containing all the
newline types seen. Universal newlines are available only when
reading. Instances support iteration in the same way as normal <a title="file" class="reference external" href="functions.html#file"><tt class="xref docutils literal"><span class="pre">file</span></tt></a>
instances.</p>
<dl class="method">
<dt id="bz2.BZ2File.close">
<tt class="descname">close</tt><big>(</big><big>)</big><a class="headerlink" href="#bz2.BZ2File.close" title="Permalink to this definition">¶</a></dt>
<dd>Close the file. Sets data attribute <tt class="xref docutils literal"><span class="pre">closed</span></tt> to true. A closed file
cannot be used for further I/O operations. <a title="bz2.BZ2File.close" class="reference internal" href="#bz2.BZ2File.close"><tt class="xref docutils literal"><span class="pre">close()</span></tt></a> may be called
more than once without error.</dd></dl>
<dl class="method">
<dt id="bz2.BZ2File.read">
<tt class="descname">read</tt><big>(</big><span class="optional">[</span><em>size</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#bz2.BZ2File.read" title="Permalink to this definition">¶</a></dt>
<dd>Read at most <em>size</em> uncompressed bytes, returned as a string. If the
<em>size</em> argument is negative or omitted, read until EOF is reached.</dd></dl>
<dl class="method">
<dt id="bz2.BZ2File.readline">
<tt class="descname">readline</tt><big>(</big><span class="optional">[</span><em>size</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#bz2.BZ2File.readline" title="Permalink to this definition">¶</a></dt>
<dd>Return the next line from the file, as a string, retaining newline. A
non-negative <em>size</em> argument limits the maximum number of bytes to return
(an incomplete line may be returned then). Return an empty string at EOF.</dd></dl>
<dl class="method">
<dt id="bz2.BZ2File.readlines">
<tt class="descname">readlines</tt><big>(</big><span class="optional">[</span><em>size</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#bz2.BZ2File.readlines" title="Permalink to this definition">¶</a></dt>
<dd>Return a list of lines read. The optional <em>size</em> argument, if given, is an
approximate bound on the total number of bytes in the lines returned.</dd></dl>
<dl class="method">
<dt id="bz2.BZ2File.xreadlines">
<tt class="descname">xreadlines</tt><big>(</big><big>)</big><a class="headerlink" href="#bz2.BZ2File.xreadlines" title="Permalink to this definition">¶</a></dt>
<dd><p>For backward compatibility. <a title="bz2.BZ2File" class="reference internal" href="#bz2.BZ2File"><tt class="xref docutils literal"><span class="pre">BZ2File</span></tt></a> objects now include the
performance optimizations previously implemented in the <tt class="xref docutils literal"><span class="pre">xreadlines</span></tt>
module.</p>
<p class="deprecated">
<span class="versionmodified">Deprecated since version 2.3: </span>This exists only for compatibility with the method by this name on
<a title="file" class="reference external" href="functions.html#file"><tt class="xref docutils literal"><span class="pre">file</span></tt></a> objects, which is deprecated. Use <tt class="docutils literal"><span class="pre">for</span> <span class="pre">line</span> <span class="pre">in</span> <span class="pre">file</span></tt>
instead.</p>
</dd></dl>
<dl class="method">
<dt id="bz2.BZ2File.seek">
<tt class="descname">seek</tt><big>(</big><em>offset</em><span class="optional">[</span>, <em>whence</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#bz2.BZ2File.seek" title="Permalink to this definition">¶</a></dt>
<dd><p>Move to new file position. Argument <em>offset</em> is a byte count. Optional
argument <em>whence</em> defaults to <tt class="docutils literal"><span class="pre">os.SEEK_SET</span></tt> or <tt class="docutils literal"><span class="pre">0</span></tt> (offset from start
of file; offset should be <tt class="docutils literal"><span class="pre">>=</span> <span class="pre">0</span></tt>); other values are <tt class="docutils literal"><span class="pre">os.SEEK_CUR</span></tt> or
<tt class="docutils literal"><span class="pre">1</span></tt> (move relative to current position; offset can be positive or
negative), and <tt class="docutils literal"><span class="pre">os.SEEK_END</span></tt> or <tt class="docutils literal"><span class="pre">2</span></tt> (move relative to end of file;
offset is usually negative, although many platforms allow seeking beyond
the end of a file).</p>
<p>Note that seeking of bz2 files is emulated, and depending on the
parameters the operation may be extremely slow.</p>
</dd></dl>
<dl class="method">
<dt id="bz2.BZ2File.tell">
<tt class="descname">tell</tt><big>(</big><big>)</big><a class="headerlink" href="#bz2.BZ2File.tell" title="Permalink to this definition">¶</a></dt>
<dd>Return the current file position, an integer (may be a long integer).</dd></dl>
<dl class="method">
<dt id="bz2.BZ2File.write">
<tt class="descname">write</tt><big>(</big><em>data</em><big>)</big><a class="headerlink" href="#bz2.BZ2File.write" title="Permalink to this definition">¶</a></dt>
<dd>Write string <em>data</em> to file. Note that due to buffering, <a title="bz2.BZ2File.close" class="reference internal" href="#bz2.BZ2File.close"><tt class="xref docutils literal"><span class="pre">close()</span></tt></a> may
be needed before the file on disk reflects the data written.</dd></dl>
<dl class="method">
<dt id="bz2.BZ2File.writelines">
<tt class="descname">writelines</tt><big>(</big><em>sequence_of_strings</em><big>)</big><a class="headerlink" href="#bz2.BZ2File.writelines" title="Permalink to this definition">¶</a></dt>
<dd>Write the sequence of strings to the file. Note that newlines are not
added. The sequence can be any iterable object producing strings. This is
equivalent to calling write() for each string.</dd></dl>
</dd></dl>
</div>
<div class="section" id="sequential-de-compression">
<h2>13.3.2. Sequential (de)compression<a class="headerlink" href="#sequential-de-compression" title="Permalink to this headline">¶</a></h2>
<p>Sequential compression and decompression is done using the classes
<a title="bz2.BZ2Compressor" class="reference internal" href="#bz2.BZ2Compressor"><tt class="xref docutils literal"><span class="pre">BZ2Compressor</span></tt></a> and <a title="bz2.BZ2Decompressor" class="reference internal" href="#bz2.BZ2Decompressor"><tt class="xref docutils literal"><span class="pre">BZ2Decompressor</span></tt></a>.</p>
<dl class="class">
<dt id="bz2.BZ2Compressor">
<em class="property">class </em><tt class="descclassname">bz2.</tt><tt class="descname">BZ2Compressor</tt><big>(</big><span class="optional">[</span><em>compresslevel</em><span class="optional">]</span><big>)</big><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
sequentially. If you want to compress data in one shot, use the
<a title="bz2.compress" class="reference internal" href="#bz2.compress"><tt class="xref docutils literal"><span class="pre">compress()</span></tt></a> function instead. The <em>compresslevel</em> parameter, if given,
must be a number between <tt class="docutils literal"><span class="pre">1</span></tt> and <tt class="docutils literal"><span class="pre">9</span></tt>; the default is <tt class="docutils literal"><span class="pre">9</span></tt>.</p>
<dl class="method">
<dt id="bz2.BZ2Compressor.compress">
<tt class="descname">compress</tt><big>(</big><em>data</em><big>)</big><a class="headerlink" href="#bz2.BZ2Compressor.compress" title="Permalink to this definition">¶</a></dt>
<dd>Provide more data to the compressor object. It will return chunks of
compressed data whenever possible. When you’ve finished providing data to
compress, call the <a title="bz2.BZ2Compressor.flush" class="reference internal" href="#bz2.BZ2Compressor.flush"><tt class="xref docutils literal"><span class="pre">flush()</span></tt></a> method to finish the compression process,
and return what is left in internal buffers.</dd></dl>
<dl class="method">
<dt id="bz2.BZ2Compressor.flush">
<tt class="descname">flush</tt><big>(</big><big>)</big><a class="headerlink" href="#bz2.BZ2Compressor.flush" title="Permalink to this definition">¶</a></dt>
<dd>Finish the compression process and return what is left in internal
buffers. You must not use the compressor object after calling this method.</dd></dl>
</dd></dl>
<dl class="class">
<dt id="bz2.BZ2Decompressor">
<em class="property">class </em><tt class="descclassname">bz2.</tt><tt class="descname">BZ2Decompressor</tt><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
sequentially. If you want to decompress data in one shot, use the
<a title="bz2.decompress" class="reference internal" href="#bz2.decompress"><tt class="xref docutils literal"><span class="pre">decompress()</span></tt></a> function instead.</p>
<dl class="method">
<dt id="bz2.BZ2Decompressor.decompress">
<tt class="descname">decompress</tt><big>(</big><em>data</em><big>)</big><a class="headerlink" href="#bz2.BZ2Decompressor.decompress" title="Permalink to this definition">¶</a></dt>
<dd>Provide more data to the decompressor object. It will return chunks of
decompressed data whenever possible. If you try to decompress data after
the end of stream is found, <a title="exceptions.EOFError" class="reference external" href="exceptions.html#exceptions.EOFError"><tt class="xref docutils literal"><span class="pre">EOFError</span></tt></a> will be raised. If any data
was found after the end of stream, it’ll be ignored and saved in
<tt class="xref docutils literal"><span class="pre">unused_data</span></tt> attribute.</dd></dl>
</dd></dl>
</div>
<div class="section" id="one-shot-de-compression">
<h2>13.3.3. One-shot (de)compression<a class="headerlink" href="#one-shot-de-compression" title="Permalink to this headline">¶</a></h2>
<p>One-shot compression and decompression is provided through the <a title="bz2.compress" class="reference internal" href="#bz2.compress"><tt class="xref docutils literal"><span class="pre">compress()</span></tt></a>
and <a title="bz2.decompress" class="reference internal" href="#bz2.decompress"><tt class="xref docutils literal"><span class="pre">decompress()</span></tt></a> functions.</p>
<dl class="function">
<dt id="bz2.compress">
<tt class="descclassname">bz2.</tt><tt class="descname">compress</tt><big>(</big><em>data</em><span class="optional">[</span>, <em>compresslevel</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#bz2.compress" title="Permalink to this definition">¶</a></dt>
<dd>Compress <em>data</em> in one shot. If you want to compress data sequentially, use
an instance of <a title="bz2.BZ2Compressor" class="reference internal" href="#bz2.BZ2Compressor"><tt class="xref docutils literal"><span class="pre">BZ2Compressor</span></tt></a> instead. The <em>compresslevel</em> parameter,
if given, must be a number between <tt class="docutils literal"><span class="pre">1</span></tt> and <tt class="docutils literal"><span class="pre">9</span></tt>; the default is <tt class="docutils literal"><span class="pre">9</span></tt>.</dd></dl>
<dl class="function">
<dt id="bz2.decompress">
<tt class="descclassname">bz2.</tt><tt class="descname">decompress</tt><big>(</big><em>data</em><big>)</big><a class="headerlink" href="#bz2.decompress" title="Permalink to this definition">¶</a></dt>
<dd>Decompress <em>data</em> in one shot. If you want to decompress data sequentially,
use an instance of <a title="bz2.BZ2Decompressor" class="reference internal" href="#bz2.BZ2Decompressor"><tt class="xref docutils literal"><span class="pre">BZ2Decompressor</span></tt></a> instead.</dd></dl>
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<h3><a href="../contents.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference external" href="#">13.3. <tt class="docutils literal"><span class="pre">bz2</span></tt> — Compression compatible with <strong>bzip2</strong></a><ul>
<li><a class="reference external" href="#de-compression-of-files">13.3.1. (De)compression of files</a></li>
<li><a class="reference external" href="#sequential-de-compression">13.3.2. Sequential (de)compression</a></li>
<li><a class="reference external" href="#one-shot-de-compression">13.3.3. One-shot (de)compression</a></li>
</ul>
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