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/usr/share/doc/python3-docs/html/library/zlib.html
(34557B)
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="X-UA-Compatible" content="IE=Edge" /> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>13.1. zlib — Compression compatible with gzip — Python 3.6.7 documentation</title> <link rel="stylesheet" href="../_static/pydoctheme.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <script type="text/javascript" id="documentation_options" data-url_root="../" src="../_static/documentation_options.js"></script> <script type="text/javascript" src="../_static/jquery.js"></script> <script type="text/javascript" src="../_static/underscore.js"></script> <script type="text/javascript" src="../_static/doctools.js"></script> <script type="text/javascript" src="../_static/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 3.6.7 documentation" href="../_static/opensearch.xml"/> <link rel="author" title="About these documents" href="../about.html" /> <link rel="index" title="Index" href="../genindex.html" /> <link rel="search" title="Search" href="../search.html" /> <link rel="copyright" title="Copyright" href="../copyright.html" /> <link rel="next" title="13.2. gzip — Support for gzip files" href="gzip.html" /> <link rel="prev" title="13. Data Compression and Archiving" href="archiving.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="https://docs.python.org/3/library/zlib.html" /> <script type="text/javascript" src="../_static/copybutton.js"></script> </head><body> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" accesskey="I">index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="gzip.html" title="13.2. gzip — Support for gzip files" accesskey="N">next</a> |</li> <li class="right" > <a href="archiving.html" title="13. 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Data Compression and Archiving</a> »</li> <li class="right"> <div class="inline-search" style="display: none" role="search"> <form class="inline-search" action="../search.html" method="get"> <input placeholder="Quick search" type="text" name="q" /> <input type="submit" value="Go" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> </div> <script type="text/javascript">$('.inline-search').show(0);</script> | </li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <div class="section" id="module-zlib"> <span id="zlib-compression-compatible-with-gzip"></span><h1>13.1. <a class="reference internal" href="#module-zlib" title="zlib: Low-level interface to compression and decompression routines compatible with gzip."><code class="xref py py-mod docutils literal notranslate"><span class="pre">zlib</span></code></a> — Compression compatible with <strong class="program">gzip</strong><a class="headerlink" href="#module-zlib" title="Permalink to this headline">¶</a></h1> <hr class="docutils" /> <p>For applications that require data compression, the functions in this module allow compression and decompression, using the zlib library. The zlib library has its own home page at <a class="reference external" href="http://www.zlib.net">http://www.zlib.net</a>. There are known incompatibilities between the Python module and versions of the zlib library earlier than 1.1.3; 1.1.3 has a security vulnerability, so we recommend using 1.1.4 or later.</p> <p>zlib’s functions have many options and often need to be used in a particular order. This documentation doesn’t attempt to cover all of the permutations; consult the zlib manual at <a class="reference external" href="http://www.zlib.net/manual.html">http://www.zlib.net/manual.html</a> for authoritative information.</p> <p>For reading and writing <code class="docutils literal notranslate"><span class="pre">.gz</span></code> files see the <a class="reference internal" href="gzip.html#module-gzip" title="gzip: Interfaces for gzip compression and decompression using file objects."><code class="xref py py-mod docutils literal notranslate"><span class="pre">gzip</span></code></a> module.</p> <p>The available exception and functions in this module are:</p> <dl class="exception"> <dt id="zlib.error"> <em class="property">exception </em><code class="descclassname">zlib.</code><code class="descname">error</code><a class="headerlink" href="#zlib.error" title="Permalink to this definition">¶</a></dt> <dd><p>Exception raised on compression and decompression errors.</p> </dd></dl> <dl class="function"> <dt id="zlib.adler32"> <code class="descclassname">zlib.</code><code class="descname">adler32</code><span class="sig-paren">(</span><em>data</em><span class="optional">[</span>, <em>value</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#zlib.adler32" title="Permalink to this definition">¶</a></dt> <dd><p>Computes an Adler-32 checksum of <em>data</em>. (An Adler-32 checksum is almost as reliable as a CRC32 but can be computed much more quickly.) The result is an unsigned 32-bit integer. If <em>value</em> is present, it is used as the starting value of the checksum; otherwise, a default value of 1 is used. Passing in <em>value</em> allows computing a running checksum over the concatenation of several inputs. The algorithm is not cryptographically strong, and should not be used for authentication or digital signatures. Since the algorithm is designed for use as a checksum algorithm, it is not suitable for use as a general hash algorithm.</p> <div class="versionchanged"> <p><span class="versionmodified">Changed in version 3.0: </span>Always returns an unsigned value. To generate the same numeric value across all Python versions and platforms, use <code class="docutils literal notranslate"><span class="pre">adler32(data)</span> <span class="pre">&</span> <span class="pre">0xffffffff</span></code>.</p> </div> </dd></dl> <dl class="function"> <dt id="zlib.compress"> <code class="descclassname">zlib.</code><code class="descname">compress</code><span class="sig-paren">(</span><em>data</em>, <em>level=-1</em><span class="sig-paren">)</span><a class="headerlink" href="#zlib.compress" title="Permalink to this definition">¶</a></dt> <dd><p>Compresses the bytes in <em>data</em>, returning a bytes object containing compressed data. <em>level</em> is an integer from <code class="docutils literal notranslate"><span class="pre">0</span></code> to <code class="docutils literal notranslate"><span class="pre">9</span></code> or <code class="docutils literal notranslate"><span class="pre">-1</span></code> controlling the level of compression; <code class="docutils literal notranslate"><span class="pre">1</span></code> (Z_BEST_SPEED) is fastest and produces the least compression, <code class="docutils literal notranslate"><span class="pre">9</span></code> (Z_BEST_COMPRESSION) is slowest and produces the most. <code class="docutils literal notranslate"><span class="pre">0</span></code> (Z_NO_COMPRESSION) is no compression. The default value is <code class="docutils literal notranslate"><span class="pre">-1</span></code> (Z_DEFAULT_COMPRESSION). Z_DEFAULT_COMPRESSION represents a default compromise between speed and compression (currently equivalent to level 6). Raises the <a class="reference internal" href="#zlib.error" title="zlib.error"><code class="xref py py-exc docutils literal notranslate"><span class="pre">error</span></code></a> exception if any error occurs.</p> <div class="versionchanged"> <p><span class="versionmodified">Changed in version 3.6: </span><em>level</em> can now be used as a keyword parameter.</p> </div> </dd></dl> <dl class="function"> <dt id="zlib.compressobj"> <code class="descclassname">zlib.</code><code class="descname">compressobj</code><span class="sig-paren">(</span><em>level=-1</em>, <em>method=DEFLATED</em>, <em>wbits=MAX_WBITS</em>, <em>memLevel=DEF_MEM_LEVEL</em>, <em>strategy=Z_DEFAULT_STRATEGY</em><span class="optional">[</span>, <em>zdict</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#zlib.compressobj" title="Permalink to this definition">¶</a></dt> <dd><p>Returns a compression object, to be used for compressing data streams that won’t fit into memory at once.</p> <p><em>level</em> is the compression level – an integer from <code class="docutils literal notranslate"><span class="pre">0</span></code> to <code class="docutils literal notranslate"><span class="pre">9</span></code> or <code class="docutils literal notranslate"><span class="pre">-1</span></code>. A value of <code class="docutils literal notranslate"><span class="pre">1</span></code> (Z_BEST_SPEED) is fastest and produces the least compression, while a value of <code class="docutils literal notranslate"><span class="pre">9</span></code> (Z_BEST_COMPRESSION) is slowest and produces the most. <code class="docutils literal notranslate"><span class="pre">0</span></code> (Z_NO_COMPRESSION) is no compression. The default value is <code class="docutils literal notranslate"><span class="pre">-1</span></code> (Z_DEFAULT_COMPRESSION). Z_DEFAULT_COMPRESSION represents a default compromise between speed and compression (currently equivalent to level 6).</p> <p><em>method</em> is the compression algorithm. Currently, the only supported value is <code class="xref py py-const docutils literal notranslate"><span class="pre">DEFLATED</span></code>.</p> <p>The <em>wbits</em> argument controls the size of the history buffer (or the “window size”) used when compressing data, and whether a header and trailer is included in the output. It can take several ranges of values, defaulting to <code class="docutils literal notranslate"><span class="pre">15</span></code> (MAX_WBITS):</p> <ul class="simple"> <li>+9 to +15: The base-two logarithm of the window size, which therefore ranges between 512 and 32768. Larger values produce better compression at the expense of greater memory usage. The resulting output will include a zlib-specific header and trailer.</li> <li>−9 to −15: Uses the absolute value of <em>wbits</em> as the window size logarithm, while producing a raw output stream with no header or trailing checksum.</li> <li>+25 to +31 = 16 + (9 to 15): Uses the low 4 bits of the value as the window size logarithm, while including a basic <strong class="program">gzip</strong> header and trailing checksum in the output.</li> </ul> <p>The <em>memLevel</em> argument controls the amount of memory used for the internal compression state. Valid values range from <code class="docutils literal notranslate"><span class="pre">1</span></code> to <code class="docutils literal notranslate"><span class="pre">9</span></code>. Higher values use more memory, but are faster and produce smaller output.</p> <p><em>strategy</em> is used to tune the compression algorithm. Possible values are <code class="xref py py-const docutils literal notranslate"><span class="pre">Z_DEFAULT_STRATEGY</span></code>, <code class="xref py py-const docutils literal notranslate"><span class="pre">Z_FILTERED</span></code>, <code class="xref py py-const docutils literal notranslate"><span class="pre">Z_HUFFMAN_ONLY</span></code>, <code class="xref py py-const docutils literal notranslate"><span class="pre">Z_RLE</span></code> (zlib 1.2.0.1) and <code class="xref py py-const docutils literal notranslate"><span class="pre">Z_FIXED</span></code> (zlib 1.2.2.2).</p> <p><em>zdict</em> is a predefined compression dictionary. This is a sequence of bytes (such as a <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) containing subsequences that are expected to occur frequently in the data that is to be compressed. Those subsequences that are expected to be most common should come at the end of the dictionary.</p> <div class="versionchanged"> <p><span class="versionmodified">Changed in version 3.3: </span>Added the <em>zdict</em> parameter and keyword argument support.</p> </div> </dd></dl> <dl class="function"> <dt id="zlib.crc32"> <code class="descclassname">zlib.</code><code class="descname">crc32</code><span class="sig-paren">(</span><em>data</em><span class="optional">[</span>, <em>value</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#zlib.crc32" title="Permalink to this definition">¶</a></dt> <dd><p id="index-0">Computes a CRC (Cyclic Redundancy Check) checksum of <em>data</em>. The result is an unsigned 32-bit integer. If <em>value</em> is present, it is used as the starting value of the checksum; otherwise, a default value of 0 is used. Passing in <em>value</em> allows computing a running checksum over the concatenation of several inputs. The algorithm is not cryptographically strong, and should not be used for authentication or digital signatures. Since the algorithm is designed for use as a checksum algorithm, it is not suitable for use as a general hash algorithm.</p> <div class="versionchanged"> <p><span class="versionmodified">Changed in version 3.0: </span>Always returns an unsigned value. To generate the same numeric value across all Python versions and platforms, use <code class="docutils literal notranslate"><span class="pre">crc32(data)</span> <span class="pre">&</span> <span class="pre">0xffffffff</span></code>.</p> </div> </dd></dl> <dl class="function"> <dt id="zlib.decompress"> <code class="descclassname">zlib.</code><code class="descname">decompress</code><span class="sig-paren">(</span><em>data</em>, <em>wbits=MAX_WBITS</em>, <em>bufsize=DEF_BUF_SIZE</em><span class="sig-paren">)</span><a class="headerlink" href="#zlib.decompress" title="Permalink to this definition">¶</a></dt> <dd><p>Decompresses the bytes in <em>data</em>, returning a bytes object containing the uncompressed data. The <em>wbits</em> parameter depends on the format of <em>data</em>, and is discussed further below. If <em>bufsize</em> is given, it is used as the initial size of the output buffer. Raises the <a class="reference internal" href="#zlib.error" title="zlib.error"><code class="xref py py-exc docutils literal notranslate"><span class="pre">error</span></code></a> exception if any error occurs.</p> <p id="decompress-wbits">The <em>wbits</em> parameter controls the size of the history buffer (or “window size”), and what header and trailer format is expected. It is similar to the parameter for <a class="reference internal" href="#zlib.compressobj" title="zlib.compressobj"><code class="xref py py-func docutils literal notranslate"><span class="pre">compressobj()</span></code></a>, but accepts more ranges of values:</p> <ul class="simple"> <li>+8 to +15: The base-two logarithm of the window size. The input must include a zlib header and trailer.</li> <li>0: Automatically determine the window size from the zlib header. Only supported since zlib 1.2.3.5.</li> <li>−8 to −15: Uses the absolute value of <em>wbits</em> as the window size logarithm. The input must be a raw stream with no header or trailer.</li> <li>+24 to +31 = 16 + (8 to 15): Uses the low 4 bits of the value as the window size logarithm. The input must include a gzip header and trailer.</li> <li>+40 to +47 = 32 + (8 to 15): Uses the low 4 bits of the value as the window size logarithm, and automatically accepts either the zlib or gzip format.</li> </ul> <p>When decompressing a stream, the window size must not be smaller than the size originally used to compress the stream; using a too-small value may result in an <a class="reference internal" href="#zlib.error" title="zlib.error"><code class="xref py py-exc docutils literal notranslate"><span class="pre">error</span></code></a> exception. The default <em>wbits</em> value corresponds to the largest window size and requires a zlib header and trailer to be included.</p> <p><em>bufsize</em> is the initial size of the buffer used to hold decompressed data. If more space is required, the buffer size will be increased as needed, so you don’t have to get this value exactly right; tuning it will only save a few calls to <code class="xref c c-func docutils literal notranslate"><span class="pre">malloc()</span></code>.</p> <div class="versionchanged"> <p><span class="versionmodified">Changed in version 3.6: </span><em>wbits</em> and <em>bufsize</em> can be used as keyword arguments.</p> </div> </dd></dl> <dl class="function"> <dt id="zlib.decompressobj"> <code class="descclassname">zlib.</code><code class="descname">decompressobj</code><span class="sig-paren">(</span><em>wbits=MAX_WBITS</em><span class="optional">[</span>, <em>zdict</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#zlib.decompressobj" title="Permalink to this definition">¶</a></dt> <dd><p>Returns a decompression object, to be used for decompressing data streams that won’t fit into memory at once.</p> <p>The <em>wbits</em> parameter controls the size of the history buffer (or the “window size”), and what header and trailer format is expected. It has the same meaning as <a class="reference external" href="#decompress-wbits">described for decompress()</a>.</p> <p>The <em>zdict</em> parameter specifies a predefined compression dictionary. If provided, this must be the same dictionary as was used by the compressor that produced the data that is to be decompressed.</p> <div class="admonition note"> <p class="first admonition-title">Note</p> <p class="last">If <em>zdict</em> is a mutable object (such as a <a class="reference internal" href="stdtypes.html#bytearray" title="bytearray"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytearray</span></code></a>), you must not modify its contents between the call to <a class="reference internal" href="#zlib.decompressobj" title="zlib.decompressobj"><code class="xref py py-func docutils literal notranslate"><span class="pre">decompressobj()</span></code></a> and the first call to the decompressor’s <code class="docutils literal notranslate"><span class="pre">decompress()</span></code> method.</p> </div> <div class="versionchanged"> <p><span class="versionmodified">Changed in version 3.3: </span>Added the <em>zdict</em> parameter.</p> </div> </dd></dl> <p>Compression objects support the following methods:</p> <dl class="method"> <dt id="zlib.Compress.compress"> <code class="descclassname">Compress.</code><code class="descname">compress</code><span class="sig-paren">(</span><em>data</em><span class="sig-paren">)</span><a class="headerlink" href="#zlib.Compress.compress" title="Permalink to this definition">¶</a></dt> <dd><p>Compress <em>data</em>, returning a bytes object containing compressed data for at least part of the data in <em>data</em>. This data should be concatenated to the output produced by any preceding calls to the <a class="reference internal" href="#zlib.compress" title="zlib.compress"><code class="xref py py-meth docutils literal notranslate"><span class="pre">compress()</span></code></a> method. Some input may be kept in internal buffers for later processing.</p> </dd></dl> <dl class="method"> <dt id="zlib.Compress.flush"> <code class="descclassname">Compress.</code><code class="descname">flush</code><span class="sig-paren">(</span><span class="optional">[</span><em>mode</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#zlib.Compress.flush" title="Permalink to this definition">¶</a></dt> <dd><p>All pending input is processed, and a bytes object containing the remaining compressed output is returned. <em>mode</em> can be selected from the constants <code class="xref py py-const docutils literal notranslate"><span class="pre">Z_NO_FLUSH</span></code>, <code class="xref py py-const docutils literal notranslate"><span class="pre">Z_PARTIAL_FLUSH</span></code>, <code class="xref py py-const docutils literal notranslate"><span class="pre">Z_SYNC_FLUSH</span></code>, <code class="xref py py-const docutils literal notranslate"><span class="pre">Z_FULL_FLUSH</span></code>, <code class="xref py py-const docutils literal notranslate"><span class="pre">Z_BLOCK</span></code> (zlib 1.2.3.4), or <code class="xref py py-const docutils literal notranslate"><span class="pre">Z_FINISH</span></code>, defaulting to <code class="xref py py-const docutils literal notranslate"><span class="pre">Z_FINISH</span></code>. Except <code class="xref py py-const docutils literal notranslate"><span class="pre">Z_FINISH</span></code>, all constants allow compressing further bytestrings of data, while <code class="xref py py-const docutils literal notranslate"><span class="pre">Z_FINISH</span></code> finishes the compressed stream and prevents compressing any more data. After calling <a class="reference internal" href="#zlib.Compress.flush" title="zlib.Compress.flush"><code class="xref py py-meth docutils literal notranslate"><span class="pre">flush()</span></code></a> with <em>mode</em> set to <code class="xref py py-const docutils literal notranslate"><span class="pre">Z_FINISH</span></code>, the <a class="reference internal" href="#zlib.compress" title="zlib.compress"><code class="xref py py-meth docutils literal notranslate"><span class="pre">compress()</span></code></a> method cannot be called again; the only realistic action is to delete the object.</p> </dd></dl> <dl class="method"> <dt id="zlib.Compress.copy"> <code class="descclassname">Compress.</code><code class="descname">copy</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#zlib.Compress.copy" title="Permalink to this definition">¶</a></dt> <dd><p>Returns a copy of the compression object. This can be used to efficiently compress a set of data that share a common initial prefix.</p> </dd></dl> <p>Decompression objects support the following methods and attributes:</p> <dl class="attribute"> <dt id="zlib.Decompress.unused_data"> <code class="descclassname">Decompress.</code><code class="descname">unused_data</code><a class="headerlink" href="#zlib.Decompress.unused_data" title="Permalink to this definition">¶</a></dt> <dd><p>A bytes object which contains any bytes past the end of the compressed data. That is, this remains <code class="docutils literal notranslate"><span class="pre">b""</span></code> until the last byte that contains compression data is available. If the whole bytestring turned out to contain compressed data, this is <code class="docutils literal notranslate"><span class="pre">b""</span></code>, an empty bytes object.</p> </dd></dl> <dl class="attribute"> <dt id="zlib.Decompress.unconsumed_tail"> <code class="descclassname">Decompress.</code><code class="descname">unconsumed_tail</code><a class="headerlink" href="#zlib.Decompress.unconsumed_tail" title="Permalink to this definition">¶</a></dt> <dd><p>A bytes object that contains any data that was not consumed by the last <a class="reference internal" href="#zlib.decompress" title="zlib.decompress"><code class="xref py py-meth docutils literal notranslate"><span class="pre">decompress()</span></code></a> call because it exceeded the limit for the uncompressed data buffer. This data has not yet been seen by the zlib machinery, so you must feed it (possibly with further data concatenated to it) back to a subsequent <a class="reference internal" href="#zlib.decompress" title="zlib.decompress"><code class="xref py py-meth docutils literal notranslate"><span class="pre">decompress()</span></code></a> method call in order to get correct output.</p> </dd></dl> <dl class="attribute"> <dt id="zlib.Decompress.eof"> <code class="descclassname">Decompress.</code><code class="descname">eof</code><a class="headerlink" href="#zlib.Decompress.eof" title="Permalink to this definition">¶</a></dt> <dd><p>A boolean indicating whether the end of the compressed data stream has been reached.</p> <p>This makes it possible to distinguish between a properly-formed compressed stream, and an incomplete or truncated one.</p> <div class="versionadded"> <p><span class="versionmodified">New in version 3.3.</span></p> </div> </dd></dl> <dl class="method"> <dt id="zlib.Decompress.decompress"> <code class="descclassname">Decompress.</code><code class="descname">decompress</code><span class="sig-paren">(</span><em>data</em>, <em>max_length=0</em><span class="sig-paren">)</span><a class="headerlink" href="#zlib.Decompress.decompress" title="Permalink to this definition">¶</a></dt> <dd><p>Decompress <em>data</em>, returning a bytes object containing the uncompressed data corresponding to at least part of the data in <em>string</em>. This data should be concatenated to the output produced by any preceding calls to the <a class="reference internal" href="#zlib.decompress" title="zlib.decompress"><code class="xref py py-meth docutils literal notranslate"><span class="pre">decompress()</span></code></a> method. Some of the input data may be preserved in internal buffers for later processing.</p> <p>If the optional parameter <em>max_length</em> is non-zero then the return value will be no longer than <em>max_length</em>. This may mean that not all of the compressed input can be processed; and unconsumed data will be stored in the attribute <a class="reference internal" href="#zlib.Decompress.unconsumed_tail" title="zlib.Decompress.unconsumed_tail"><code class="xref py py-attr docutils literal notranslate"><span class="pre">unconsumed_tail</span></code></a>. This bytestring must be passed to a subsequent call to <a class="reference internal" href="#zlib.decompress" title="zlib.decompress"><code class="xref py py-meth docutils literal notranslate"><span class="pre">decompress()</span></code></a> if decompression is to continue. If <em>max_length</em> is zero then the whole input is decompressed, and <a class="reference internal" href="#zlib.Decompress.unconsumed_tail" title="zlib.Decompress.unconsumed_tail"><code class="xref py py-attr docutils literal notranslate"><span class="pre">unconsumed_tail</span></code></a> is empty.</p> <div class="versionchanged"> <p><span class="versionmodified">Changed in version 3.6: </span><em>max_length</em> can be used as a keyword argument.</p> </div> </dd></dl> <dl class="method"> <dt id="zlib.Decompress.flush"> <code class="descclassname">Decompress.</code><code class="descname">flush</code><span class="sig-paren">(</span><span class="optional">[</span><em>length</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#zlib.Decompress.flush" title="Permalink to this definition">¶</a></dt> <dd><p>All pending input is processed, and a bytes object containing the remaining uncompressed output is returned. After calling <a class="reference internal" href="#zlib.Decompress.flush" title="zlib.Decompress.flush"><code class="xref py py-meth docutils literal notranslate"><span class="pre">flush()</span></code></a>, the <a class="reference internal" href="#zlib.decompress" title="zlib.decompress"><code class="xref py py-meth docutils literal notranslate"><span class="pre">decompress()</span></code></a> method cannot be called again; the only realistic action is to delete the object.</p> <p>The optional parameter <em>length</em> sets the initial size of the output buffer.</p> </dd></dl> <dl class="method"> <dt id="zlib.Decompress.copy"> <code class="descclassname">Decompress.</code><code class="descname">copy</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#zlib.Decompress.copy" title="Permalink to this definition">¶</a></dt> <dd><p>Returns a copy of the decompression object. This can be used to save the state of the decompressor midway through the data stream in order to speed up random seeks into the stream at a future point.</p> </dd></dl> <p>Information about the version of the zlib library in use is available through the following constants:</p> <dl class="data"> <dt id="zlib.ZLIB_VERSION"> <code class="descclassname">zlib.</code><code class="descname">ZLIB_VERSION</code><a class="headerlink" href="#zlib.ZLIB_VERSION" title="Permalink to this definition">¶</a></dt> <dd><p>The version string of the zlib library that was used for building the module. This may be different from the zlib library actually used at runtime, which is available as <a class="reference internal" href="#zlib.ZLIB_RUNTIME_VERSION" title="zlib.ZLIB_RUNTIME_VERSION"><code class="xref py py-const docutils literal notranslate"><span class="pre">ZLIB_RUNTIME_VERSION</span></code></a>.</p> </dd></dl> <dl class="data"> <dt id="zlib.ZLIB_RUNTIME_VERSION"> <code class="descclassname">zlib.</code><code class="descname">ZLIB_RUNTIME_VERSION</code><a class="headerlink" href="#zlib.ZLIB_RUNTIME_VERSION" title="Permalink to this definition">¶</a></dt> <dd><p>The version string of the zlib library actually loaded by the interpreter.</p> <div class="versionadded"> <p><span class="versionmodified">New in version 3.3.</span></p> </div> </dd></dl> <div class="admonition seealso"> <p class="first admonition-title">See also</p> <dl class="last docutils"> <dt>Module <a class="reference internal" href="gzip.html#module-gzip" title="gzip: Interfaces for gzip compression and decompression using file objects."><code class="xref py py-mod docutils literal notranslate"><span class="pre">gzip</span></code></a></dt> <dd>Reading and writing <strong class="program">gzip</strong>-format files.</dd> <dt><a class="reference external" href="http://www.zlib.net">http://www.zlib.net</a></dt> <dd>The zlib library home page.</dd> <dt><a class="reference external" href="http://www.zlib.net/manual.html">http://www.zlib.net/manual.html</a></dt> <dd>The zlib manual explains the semantics and usage of the library’s many functions.</dd> </dl> </div> </div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="main navigation"> <div class="sphinxsidebarwrapper"> <h4>Previous topic</h4> <p class="topless"><a href="archiving.html" title="previous chapter">13. Data Compression and Archiving</a></p> <h4>Next topic</h4> <p class="topless"><a href="gzip.html" title="next chapter">13.2. <code class="docutils literal notranslate"><span class="pre">gzip</span></code> — Support for <strong class="program">gzip</strong> files</a></p> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../bugs.html">Report a Bug</a></li> <li> <a href="https://github.com/python/cpython/blob/3.6/Doc/library/zlib.rst" rel="nofollow">Show Source </a> </li> </ul> </div> </div> </div> <div class="clearer"></div> </div> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" >index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="gzip.html" title="13.2. gzip — Support for gzip files" >next</a> |</li> <li class="right" > <a href="archiving.html" title="13. 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