CINXE.COM

<!DOCTYPE html> <html lang="en" data-content_root="../"> <head> <meta charset="utf-8" /> <meta name="viewport" content="width=device-width, initial-scale=1.0" /><meta name="viewport" content="width=device-width, initial-scale=1" /> <meta property="og:title" content="zlib — Compression compatible with gzip" /> <meta property="og:type" content="website" /> <meta property="og:url" content="https://docs.python.org/3/library/zlib.html" /> <meta property="og:site_name" content="Python documentation" /> <meta property="og:description" content="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 https://www.zlib...." /> <meta property="og:image" content="https://docs.python.org/3/_static/og-image.png" /> <meta property="og:image:alt" content="Python documentation" /> <meta name="description" content="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 https://www.zlib...." /> <meta property="og:image:width" content="200" /> <meta property="og:image:height" content="200" /> <meta name="theme-color" content="#3776ab" /> <title>zlib — Compression compatible with gzip — Python 3.13.2 documentation</title><meta name="viewport" content="width=device-width, initial-scale=1.0"> <link rel="stylesheet" type="text/css" href="../_static/pygments.css?v=b86133f3" /> <link rel="stylesheet" type="text/css" href="../_static/pydoctheme.css?v=23252803" /> <link id="pygments_dark_css" media="(prefers-color-scheme: dark)" rel="stylesheet" type="text/css" href="../_static/pygments_dark.css?v=5349f25f" /> <script src="../_static/documentation_options.js?v=f92f4e34"></script> <script src="../_static/doctools.js?v=9bcbadda"></script> <script src="../_static/sphinx_highlight.js?v=dc90522c"></script> <script src="../_static/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 3.13.2 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="gzip — Support for gzip files" href="gzip.html" /> <link rel="prev" title="Data Compression and Archiving" href="archiving.html" /> <script defer data-domain="docs.python.org" src="https://plausible.io/js/script.js"></script> <link rel="canonical" href="https://docs.python.org/3/library/zlib.html" /> <style> @media only screen { table.full-width-table { width: 100%; } } </style> <link rel="stylesheet" href="../_static/pydoctheme_dark.css" media="(prefers-color-scheme: dark)" id="pydoctheme_dark_css"> <link rel="shortcut icon" type="image/png" href="../_static/py.svg" /> <script type="text/javascript" src="../_static/copybutton.js"></script> <script type="text/javascript" src="../_static/menu.js"></script> <script type="text/javascript" src="../_static/search-focus.js"></script> <script type="text/javascript" src="../_static/themetoggle.js"></script> <script type="text/javascript" src="../_static/rtd_switcher.js"></script> <meta name="readthedocs-addons-api-version" content="1"> </head> <body> <div class="mobile-nav"> <input type="checkbox" id="menuToggler" class="toggler__input" aria-controls="navigation" aria-pressed="false" aria-expanded="false" role="button" aria-label="Menu" /> <nav class="nav-content" role="navigation"> <label for="menuToggler" class="toggler__label"> </label> <a href="https://www.python.org/" class="nav-logo"> <img src="../_static/py.svg" alt="Python logo"/> </a> <form role="search" class="search" action="../search.html" method="get"> <svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 24 24" class="search-icon"> <path fill-rule="nonzero" fill="currentColor" d="M15.5 14h-.79l-.28-.27a6.5 6.5 0 001.48-5.34c-.47-2.78-2.79-5-5.59-5.34a6.505 6.505 0 00-7.27 7.27c.34 2.8 2.56 5.12 5.34 5.59a6.5 6.5 0 005.34-1.48l.27.28v.79l4.25 4.25c.41.41 1.08.41 1.49 0 .41-.41.41-1.08 0-1.49L15.5 14zm-6 0C7.01 14 5 11.99 5 9.5S7.01 5 9.5 5 14 7.01 14 9.5 11.99 14 9.5 14z"></path> </svg> <input placeholder="Quick search" aria-label="Quick search" type="search" name="q" /> <input type="submit" value="Go"/> </form> </nav> <div class="menu-wrapper"> <nav class="menu" role="navigation" aria-label="main navigation"> <div class="language_switcher_placeholder"></div> <label class="theme-selector-label"> Theme <select class="theme-selector" oninput="activateTheme(this.value)"> <option value="auto" selected>Auto</option> <option value="light">Light</option> <option value="dark">Dark</option> </select> </label> <div> <h4>Previous topic</h4> <a href="archiving.html" title="previous chapter">Data Compression and Archiving</a> </div> <div> <h4>Next topic</h4> <a href="gzip.html" title="next chapter"><code class="xref py py-mod docutils literal notranslate">gzip</code> — Support for gzip files</a> </div> <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/main/Doc/library/zlib.rst" rel="nofollow">Show Source </a> </li> </ul> </div> </nav> </div> </div> <div class="related" role="navigation" aria-label="Related"> <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="gzip — Support for gzip files" accesskey="N">next</a> |</li> <li class="right" > <a href="archiving.html" title="Data Compression and Archiving" accesskey="P">previous</a> |</li> <li><img src="../_static/py.svg" alt="Python logo" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li class="switchers"> <div class="language_switcher_placeholder"></div> <div class="version_switcher_placeholder"></div> </li> <li> </li> <li id="cpython-language-and-version"> <a href="../index.html">3.13.2 Documentation</a> » </li> <li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> »</li> <li class="nav-item nav-item-2"><a href="archiving.html" accesskey="U">Data Compression and Archiving</a> »</li> <li class="nav-item nav-item-this"><a href=""><code class="xref py py-mod docutils literal notranslate">zlib</code> — Compression compatible with gzip</a></li> <li class="right"> <div class="inline-search" role="search"> <form class="inline-search" action="../search.html" method="get"> <input placeholder="Quick search" aria-label="Quick search" type="search" name="q" id="search-box" /> <input type="submit" value="Go" /> </form> </div> | </li> <li class="right"> <label class="theme-selector-label"> Theme <select class="theme-selector" oninput="activateTheme(this.value)"> <option value="auto" selected>Auto</option> <option value="light">Light</option> <option value="dark">Dark</option> </select> </label> |</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <section id="module-zlib"> <h1><code class="xref py py-mod docutils literal notranslate">zlib</code> — Compression compatible with gzip<a class="headerlink" href="#module-zlib" title="Link to this heading">¶</a></h1> <hr class="docutils" /> 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="https://www.zlib.net">https://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 <a class="reference external" href="https://zlib.net/zlib_faq.html#faq33">security vulnerability</a>, so we recommend using 1.1.4 or later. 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. For reading and writing <code class="docutils literal notranslate">.gz</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">gzip</code></a> module. The available exception and functions in this module are: <dl class="py exception"> <dt class="sig sig-object py" id="zlib.error"> exception zlib.error<a class="headerlink" href="#zlib.error" title="Link to this definition">¶</a></dt> <dd>Exception raised on compression and decompression errors. </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="zlib.adler32"> zlib.adler32(data[, value])<a class="headerlink" href="#zlib.adler32" title="Link to this definition">¶</a></dt> <dd>Computes an Adler-32 checksum of data. (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 value is present, it is used as the starting value of the checksum; otherwise, a default value of 1 is used. Passing in value 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. <div class="versionchanged"> Changed in version 3.0: The result is always unsigned. </div> </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="zlib.compress"> zlib.compress(data, /, level=-1, wbits=MAX_WBITS)<a class="headerlink" href="#zlib.compress" title="Link to this definition">¶</a></dt> <dd>Compresses the bytes in data, returning a bytes object containing compressed data. level is an integer from <code class="docutils literal notranslate">0</code> to <code class="docutils literal notranslate">9</code> or <code class="docutils literal notranslate">-1</code> controlling the level of compression; <code class="docutils literal notranslate">1</code> (Z_BEST_SPEED) is fastest and produces the least compression, <code class="docutils literal notranslate">9</code> (Z_BEST_COMPRESSION) is slowest and produces the most. <code class="docutils literal notranslate">0</code> (Z_NO_COMPRESSION) is no compression. The default value is <code class="docutils literal notranslate">-1</code> (Z_DEFAULT_COMPRESSION). Z_DEFAULT_COMPRESSION represents a default compromise between speed and compression (currently equivalent to level 6). The wbits 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">15</code> (MAX_WBITS): <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 wbits 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 gzip header and trailing checksum in the output.</li> </ul> Raises the <a class="reference internal" href="#zlib.error" title="zlib.error"><code class="xref py py-exc docutils literal notranslate">error</code></a> exception if any error occurs. <div class="versionchanged"> Changed in version 3.6: level can now be used as a keyword parameter. </div> <div class="versionchanged"> Changed in version 3.11: The wbits parameter is now available to set window bits and compression type. </div> </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="zlib.compressobj"> zlib.compressobj(level=-1, method=DEFLATED, wbits=MAX_WBITS, memLevel=DEF_MEM_LEVEL, strategy=Z_DEFAULT_STRATEGY[, zdict])<a class="headerlink" href="#zlib.compressobj" title="Link to this definition">¶</a></dt> <dd>Returns a compression object, to be used for compressing data streams that won’t fit into memory at once. level is the compression level – an integer from <code class="docutils literal notranslate">0</code> to <code class="docutils literal notranslate">9</code> or <code class="docutils literal notranslate">-1</code>. A value of <code class="docutils literal notranslate">1</code> (Z_BEST_SPEED) is fastest and produces the least compression, while a value of <code class="docutils literal notranslate">9</code> (Z_BEST_COMPRESSION) is slowest and produces the most. <code class="docutils literal notranslate">0</code> (Z_NO_COMPRESSION) is no compression. The default value is <code class="docutils literal notranslate">-1</code> (Z_DEFAULT_COMPRESSION). Z_DEFAULT_COMPRESSION represents a default compromise between speed and compression (currently equivalent to level 6). method is the compression algorithm. Currently, the only supported value is <code class="xref py py-const docutils literal notranslate">DEFLATED</code>. The wbits parameter controls the size of the history buffer (or the “window size”), and what header and trailer format will be used. It has the same meaning as <a class="reference external" href="#compress-wbits">described for compress()</a>. The memLevel argument controls the amount of memory used for the internal compression state. Valid values range from <code class="docutils literal notranslate">1</code> to <code class="docutils literal notranslate">9</code>. Higher values use more memory, but are faster and produce smaller output. strategy is used to tune the compression algorithm. Possible values are <code class="xref py py-const docutils literal notranslate">Z_DEFAULT_STRATEGY</code>, <code class="xref py py-const docutils literal notranslate">Z_FILTERED</code>, <code class="xref py py-const docutils literal notranslate">Z_HUFFMAN_ONLY</code>, <code class="xref py py-const docutils literal notranslate">Z_RLE</code> (zlib 1.2.0.1) and <code class="xref py py-const docutils literal notranslate">Z_FIXED</code> (zlib 1.2.2.2). zdict 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">bytes</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. <div class="versionchanged"> Changed in version 3.3: Added the zdict parameter and keyword argument support. </div> </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="zlib.crc32"> zlib.crc32(data[, value])<a class="headerlink" href="#zlib.crc32" title="Link to this definition">¶</a></dt> <dd>Computes a CRC (Cyclic Redundancy Check) checksum of data. The result is an unsigned 32-bit integer. If value is present, it is used as the starting value of the checksum; otherwise, a default value of 0 is used. Passing in value 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. <div class="versionchanged"> Changed in version 3.0: The result is always unsigned. </div> </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="zlib.decompress"> zlib.decompress(data, /, wbits=MAX_WBITS, bufsize=DEF_BUF_SIZE)<a class="headerlink" href="#zlib.decompress" title="Link to this definition">¶</a></dt> <dd>Decompresses the bytes in data, returning a bytes object containing the uncompressed data. The wbits parameter depends on the format of data, and is discussed further below. If bufsize 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">error</code></a> exception if any error occurs. The wbits 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">compressobj()</code></a>, but accepts more ranges of values: <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 wbits 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> 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">error</code></a> exception. The default wbits value corresponds to the largest window size and requires a zlib header and trailer to be included. bufsize 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">malloc()</code>. <div class="versionchanged"> Changed in version 3.6: wbits and bufsize can be used as keyword arguments. </div> </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="zlib.decompressobj"> zlib.decompressobj(wbits=MAX_WBITS[, zdict])<a class="headerlink" href="#zlib.decompressobj" title="Link to this definition">¶</a></dt> <dd>Returns a decompression object, to be used for decompressing data streams that won’t fit into memory at once. The wbits 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>. The zdict 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. <div class="admonition note"> Note If zdict 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">bytearray</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">decompressobj()</code></a> and the first call to the decompressor’s <code class="docutils literal notranslate">decompress()</code> method. </div> <div class="versionchanged"> Changed in version 3.3: Added the zdict parameter. </div> </dd></dl> Compression objects support the following methods: <dl class="py method"> <dt class="sig sig-object py" id="zlib.Compress.compress"> Compress.compress(data)<a class="headerlink" href="#zlib.Compress.compress" title="Link to this definition">¶</a></dt> <dd>Compress data, returning a bytes object containing compressed data for at least part of the data in data. 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">compress()</code></a> method. Some input may be kept in internal buffers for later processing. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="zlib.Compress.flush"> Compress.flush([mode])<a class="headerlink" href="#zlib.Compress.flush" title="Link to this definition">¶</a></dt> <dd>All pending input is processed, and a bytes object containing the remaining compressed output is returned. mode can be selected from the constants <code class="xref py py-const docutils literal notranslate">Z_NO_FLUSH</code>, <code class="xref py py-const docutils literal notranslate">Z_PARTIAL_FLUSH</code>, <code class="xref py py-const docutils literal notranslate">Z_SYNC_FLUSH</code>, <code class="xref py py-const docutils literal notranslate">Z_FULL_FLUSH</code>, <code class="xref py py-const docutils literal notranslate">Z_BLOCK</code> (zlib 1.2.3.4), or <code class="xref py py-const docutils literal notranslate">Z_FINISH</code>, defaulting to <code class="xref py py-const docutils literal notranslate">Z_FINISH</code>. Except <code class="xref py py-const docutils literal notranslate">Z_FINISH</code>, all constants allow compressing further bytestrings of data, while <code class="xref py py-const docutils literal notranslate">Z_FINISH</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">flush()</code></a> with mode set to <code class="xref py py-const docutils literal notranslate">Z_FINISH</code>, the <a class="reference internal" href="#zlib.compress" title="zlib.compress"><code class="xref py py-meth docutils literal notranslate">compress()</code></a> method cannot be called again; the only realistic action is to delete the object. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="zlib.Compress.copy"> Compress.copy()<a class="headerlink" href="#zlib.Compress.copy" title="Link to this definition">¶</a></dt> <dd>Returns a copy of the compression object. This can be used to efficiently compress a set of data that share a common initial prefix. </dd></dl> <div class="versionchanged"> Changed in version 3.8: Added <a class="reference internal" href="copy.html#copy.copy" title="copy.copy"><code class="xref py py-func docutils literal notranslate">copy.copy()</code></a> and <a class="reference internal" href="copy.html#copy.deepcopy" title="copy.deepcopy"><code class="xref py py-func docutils literal notranslate">copy.deepcopy()</code></a> support to compression objects. </div> Decompression objects support the following methods and attributes: <dl class="py attribute"> <dt class="sig sig-object py" id="zlib.Decompress.unused_data"> Decompress.unused_data<a class="headerlink" href="#zlib.Decompress.unused_data" title="Link to this definition">¶</a></dt> <dd>A bytes object which contains any bytes past the end of the compressed data. That is, this remains <code class="docutils literal notranslate">b""</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">b""</code>, an empty bytes object. </dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="zlib.Decompress.unconsumed_tail"> Decompress.unconsumed_tail<a class="headerlink" href="#zlib.Decompress.unconsumed_tail" title="Link to this definition">¶</a></dt> <dd>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">decompress()</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">decompress()</code></a> method call in order to get correct output. </dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="zlib.Decompress.eof"> Decompress.eof<a class="headerlink" href="#zlib.Decompress.eof" title="Link to this definition">¶</a></dt> <dd>A boolean indicating whether the end of the compressed data stream has been reached. This makes it possible to distinguish between a properly formed compressed stream, and an incomplete or truncated one. <div class="versionadded"> Added in version 3.3. </div> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="zlib.Decompress.decompress"> Decompress.decompress(data, max_length=0)<a class="headerlink" href="#zlib.Decompress.decompress" title="Link to this definition">¶</a></dt> <dd>Decompress data, returning a bytes object containing the uncompressed data corresponding to at least part of the data in string. 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">decompress()</code></a> method. Some of the input data may be preserved in internal buffers for later processing. If the optional parameter max_length is non-zero then the return value will be no longer than max_length. 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">unconsumed_tail</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">decompress()</code></a> if decompression is to continue. If max_length 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">unconsumed_tail</code></a> is empty. <div class="versionchanged"> Changed in version 3.6: max_length can be used as a keyword argument. </div> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="zlib.Decompress.flush"> Decompress.flush([length])<a class="headerlink" href="#zlib.Decompress.flush" title="Link to this definition">¶</a></dt> <dd>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">flush()</code></a>, the <a class="reference internal" href="#zlib.decompress" title="zlib.decompress"><code class="xref py py-meth docutils literal notranslate">decompress()</code></a> method cannot be called again; the only realistic action is to delete the object. The optional parameter length sets the initial size of the output buffer. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="zlib.Decompress.copy"> Decompress.copy()<a class="headerlink" href="#zlib.Decompress.copy" title="Link to this definition">¶</a></dt> <dd>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. </dd></dl> <div class="versionchanged"> Changed in version 3.8: Added <a class="reference internal" href="copy.html#copy.copy" title="copy.copy"><code class="xref py py-func docutils literal notranslate">copy.copy()</code></a> and <a class="reference internal" href="copy.html#copy.deepcopy" title="copy.deepcopy"><code class="xref py py-func docutils literal notranslate">copy.deepcopy()</code></a> support to decompression objects. </div> Information about the version of the zlib library in use is available through the following constants: <dl class="py data"> <dt class="sig sig-object py" id="zlib.ZLIB_VERSION"> zlib.ZLIB_VERSION<a class="headerlink" href="#zlib.ZLIB_VERSION" title="Link to this definition">¶</a></dt> <dd>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">ZLIB_RUNTIME_VERSION</code></a>. </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="zlib.ZLIB_RUNTIME_VERSION"> zlib.ZLIB_RUNTIME_VERSION<a class="headerlink" href="#zlib.ZLIB_RUNTIME_VERSION" title="Link to this definition">¶</a></dt> <dd>The version string of the zlib library actually loaded by the interpreter. <div class="versionadded"> Added in version 3.3. </div> </dd></dl> <div class="admonition seealso"> See also <dl class="simple"> <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">gzip</code></a></dt><dd>Reading and writing gzip-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> </section> <div class="clearer"></div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="Main"> <div class="sphinxsidebarwrapper"> <div> <h4>Previous topic</h4> <a href="archiving.html" title="previous chapter">Data Compression and Archiving</a> </div> <div> <h4>Next topic</h4> <a href="gzip.html" title="next chapter"><code class="xref py py-mod docutils literal notranslate">gzip</code> — Support for gzip files</a> </div> <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/main/Doc/library/zlib.rst" rel="nofollow">Show Source </a> </li> </ul> </div> </div> <div id="sidebarbutton" title="Collapse sidebar"> « </div> </div> <div class="clearer"></div> </div> <div class="related" role="navigation" aria-label="Related"> <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="gzip — Support for gzip files" >next</a> |</li> <li class="right" > <a href="archiving.html" title="Data Compression and Archiving" >previous</a> |</li> <li><img src="../_static/py.svg" alt="Python logo" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li class="switchers"> <div class="language_switcher_placeholder"></div> <div class="version_switcher_placeholder"></div> </li> <li> </li> <li id="cpython-language-and-version"> <a href="../index.html">3.13.2 Documentation</a> » </li> <li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> »</li> <li class="nav-item nav-item-2"><a href="archiving.html" >Data Compression and Archiving</a> »</li> <li class="nav-item nav-item-this"><a href=""><code class="xref py py-mod docutils literal notranslate">zlib</code> — Compression compatible with gzip</a></li> <li class="right"> <div class="inline-search" role="search"> <form class="inline-search" action="../search.html" method="get"> <input placeholder="Quick search" aria-label="Quick search" type="search" name="q" id="search-box" /> <input type="submit" value="Go" /> </form> </div> | </li> <li class="right"> <label class="theme-selector-label"> Theme <select class="theme-selector" oninput="activateTheme(this.value)"> <option value="auto" selected>Auto</option> <option value="light">Light</option> <option value="dark">Dark</option> </select> </label> |</li> </ul> </div> <div class="footer"> © <a href="../copyright.html"> Copyright </a> 2001-2025, Python Software Foundation. This page is licensed under the Python Software Foundation License Version 2. Examples, recipes, and other code in the documentation are additionally licensed under the Zero Clause BSD License. See <a href="/license.html">History and License</a> for more information. The Python Software Foundation is a non-profit corporation. <a href="https://www.python.org/psf/donations/">Please donate.</a> Last updated on Feb 17, 2025 (16:47 UTC). <a href="/bugs.html">Found a bug</a>? Created using <a href="https://www.sphinx-doc.org/">Sphinx</a> 8.1.3. </div> <script type="text/javascript" src="../_static/switchers.js"></script> </body> </html>