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<!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="Content-Type" content="text/html; charset=utf-8" /> <title>7.8. codecs — Codec registry and base classes — Python 2.7.5 documentation</title> <link rel="stylesheet" href="../_static/default.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <script type="text/javascript"> var DOCUMENTATION_OPTIONS = { URL_ROOT: '../', VERSION: '2.7.5', COLLAPSE_INDEX: false, FILE_SUFFIX: '.html', HAS_SOURCE: true }; </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 2.7.5 documentation" href="../_static/opensearch.xml"/> <link rel="author" title="About these documents" href="../about.html" /> <link rel="copyright" title="Copyright" href="../copyright.html" /> <link rel="top" title="Python 2.7.5 documentation" href="../index.html" /> <link rel="up" title="7. 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String Services</a> »</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body"> <div class="section" id="module-codecs"> <span id="codecs-codec-registry-and-base-classes"></span><h1>7.8. <a class="reference internal" href="#module-codecs" title="codecs: Encode and decode data and streams."><tt class="xref py py-mod docutils literal"><span class="pre">codecs</span></tt></a> — Codec registry and base classes<a class="headerlink" href="#module-codecs" title="Permalink to this headline">¶</a></h1> <p id="index-0">This module defines base classes for standard Python codecs (encoders and decoders) and provides access to the internal Python codec registry which manages the codec and error handling lookup process.</p> <p>It defines the following functions:</p> <dl class="function"> <dt id="codecs.register"> <tt class="descclassname">codecs.</tt><tt class="descname">register</tt><big>(</big><em>search_function</em><big>)</big><a class="headerlink" href="#codecs.register" title="Permalink to this definition">¶</a></dt> <dd><p>Register a codec search function. Search functions are expected to take one argument, the encoding name in all lower case letters, and return a <tt class="xref py py-class docutils literal"><span class="pre">CodecInfo</span></tt> object having the following attributes:</p> <ul class="simple"> <li><tt class="docutils literal"><span class="pre">name</span></tt> The name of the encoding;</li> <li><tt class="docutils literal"><span class="pre">encode</span></tt> The stateless encoding function;</li> <li><tt class="docutils literal"><span class="pre">decode</span></tt> The stateless decoding function;</li> <li><tt class="docutils literal"><span class="pre">incrementalencoder</span></tt> An incremental encoder class or factory function;</li> <li><tt class="docutils literal"><span class="pre">incrementaldecoder</span></tt> An incremental decoder class or factory function;</li> <li><tt class="docutils literal"><span class="pre">streamwriter</span></tt> A stream writer class or factory function;</li> <li><tt class="docutils literal"><span class="pre">streamreader</span></tt> A stream reader class or factory function.</li> </ul> <p>The various functions or classes take the following arguments:</p> <p><em>encode</em> and <em>decode</em>: These must be functions or methods which have the same interface as the <tt class="xref py py-meth docutils literal"><span class="pre">encode()</span></tt>/<tt class="xref py py-meth docutils literal"><span class="pre">decode()</span></tt> methods of Codec instances (see Codec Interface). The functions/methods are expected to work in a stateless mode.</p> <p><em>incrementalencoder</em> and <em>incrementaldecoder</em>: These have to be factory functions providing the following interface:</p> <blockquote> <div><tt class="docutils literal"><span class="pre">factory(errors='strict')</span></tt></div></blockquote> <p>The factory functions must return objects providing the interfaces defined by the base classes <a class="reference internal" href="#codecs.IncrementalEncoder" title="codecs.IncrementalEncoder"><tt class="xref py py-class docutils literal"><span class="pre">IncrementalEncoder</span></tt></a> and <a class="reference internal" href="#codecs.IncrementalDecoder" title="codecs.IncrementalDecoder"><tt class="xref py py-class docutils literal"><span class="pre">IncrementalDecoder</span></tt></a>, respectively. Incremental codecs can maintain state.</p> <p><em>streamreader</em> and <em>streamwriter</em>: These have to be factory functions providing the following interface:</p> <blockquote> <div><tt class="docutils literal"><span class="pre">factory(stream,</span> <span class="pre">errors='strict')</span></tt></div></blockquote> <p>The factory functions must return objects providing the interfaces defined by the base classes <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><tt class="xref py py-class docutils literal"><span class="pre">StreamWriter</span></tt></a> and <a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><tt class="xref py py-class docutils literal"><span class="pre">StreamReader</span></tt></a>, respectively. Stream codecs can maintain state.</p> <p>Possible values for errors are</p> <ul class="simple"> <li><tt class="docutils literal"><span class="pre">'strict'</span></tt>: raise an exception in case of an encoding error</li> <li><tt class="docutils literal"><span class="pre">'replace'</span></tt>: replace malformed data with a suitable replacement marker, such as <tt class="docutils literal"><span class="pre">'?'</span></tt> or <tt class="docutils literal"><span class="pre">'\ufffd'</span></tt></li> <li><tt class="docutils literal"><span class="pre">'ignore'</span></tt>: ignore malformed data and continue without further notice</li> <li><tt class="docutils literal"><span class="pre">'xmlcharrefreplace'</span></tt>: replace with the appropriate XML character reference (for encoding only)</li> <li><tt class="docutils literal"><span class="pre">'backslashreplace'</span></tt>: replace with backslashed escape sequences (for encoding only)</li> </ul> <p>as well as any other error handling name defined via <a class="reference internal" href="#codecs.register_error" title="codecs.register_error"><tt class="xref py py-func docutils literal"><span class="pre">register_error()</span></tt></a>.</p> <p>In case a search function cannot find a given encoding, it should return <tt class="docutils literal"><span class="pre">None</span></tt>.</p> </dd></dl> <dl class="function"> <dt id="codecs.lookup"> <tt class="descclassname">codecs.</tt><tt class="descname">lookup</tt><big>(</big><em>encoding</em><big>)</big><a class="headerlink" href="#codecs.lookup" title="Permalink to this definition">¶</a></dt> <dd><p>Looks up the codec info in the Python codec registry and returns a <tt class="xref py py-class docutils literal"><span class="pre">CodecInfo</span></tt> object as defined above.</p> <p>Encodings are first looked up in the registry’s cache. If not found, the list of registered search functions is scanned. If no <tt class="xref py py-class docutils literal"><span class="pre">CodecInfo</span></tt> object is found, a <a class="reference internal" href="exceptions.html#exceptions.LookupError" title="exceptions.LookupError"><tt class="xref py py-exc docutils literal"><span class="pre">LookupError</span></tt></a> is raised. Otherwise, the <tt class="xref py py-class docutils literal"><span class="pre">CodecInfo</span></tt> object is stored in the cache and returned to the caller.</p> </dd></dl> <p>To simplify access to the various codecs, the module provides these additional functions which use <a class="reference internal" href="#codecs.lookup" title="codecs.lookup"><tt class="xref py py-func docutils literal"><span class="pre">lookup()</span></tt></a> for the codec lookup:</p> <dl class="function"> <dt id="codecs.getencoder"> <tt class="descclassname">codecs.</tt><tt class="descname">getencoder</tt><big>(</big><em>encoding</em><big>)</big><a class="headerlink" href="#codecs.getencoder" title="Permalink to this definition">¶</a></dt> <dd><p>Look up the codec for the given encoding and return its encoder function.</p> <p>Raises a <a class="reference internal" href="exceptions.html#exceptions.LookupError" title="exceptions.LookupError"><tt class="xref py py-exc docutils literal"><span class="pre">LookupError</span></tt></a> in case the encoding cannot be found.</p> </dd></dl> <dl class="function"> <dt id="codecs.getdecoder"> <tt class="descclassname">codecs.</tt><tt class="descname">getdecoder</tt><big>(</big><em>encoding</em><big>)</big><a class="headerlink" href="#codecs.getdecoder" title="Permalink to this definition">¶</a></dt> <dd><p>Look up the codec for the given encoding and return its decoder function.</p> <p>Raises a <a class="reference internal" href="exceptions.html#exceptions.LookupError" title="exceptions.LookupError"><tt class="xref py py-exc docutils literal"><span class="pre">LookupError</span></tt></a> in case the encoding cannot be found.</p> </dd></dl> <dl class="function"> <dt id="codecs.getincrementalencoder"> <tt class="descclassname">codecs.</tt><tt class="descname">getincrementalencoder</tt><big>(</big><em>encoding</em><big>)</big><a class="headerlink" href="#codecs.getincrementalencoder" title="Permalink to this definition">¶</a></dt> <dd><p>Look up the codec for the given encoding and return its incremental encoder class or factory function.</p> <p>Raises a <a class="reference internal" href="exceptions.html#exceptions.LookupError" title="exceptions.LookupError"><tt class="xref py py-exc docutils literal"><span class="pre">LookupError</span></tt></a> in case the encoding cannot be found or the codec doesn’t support an incremental encoder.</p> <p class="versionadded"> <span class="versionmodified">New in version 2.5.</span></p> </dd></dl> <dl class="function"> <dt id="codecs.getincrementaldecoder"> <tt class="descclassname">codecs.</tt><tt class="descname">getincrementaldecoder</tt><big>(</big><em>encoding</em><big>)</big><a class="headerlink" href="#codecs.getincrementaldecoder" title="Permalink to this definition">¶</a></dt> <dd><p>Look up the codec for the given encoding and return its incremental decoder class or factory function.</p> <p>Raises a <a class="reference internal" href="exceptions.html#exceptions.LookupError" title="exceptions.LookupError"><tt class="xref py py-exc docutils literal"><span class="pre">LookupError</span></tt></a> in case the encoding cannot be found or the codec doesn’t support an incremental decoder.</p> <p class="versionadded"> <span class="versionmodified">New in version 2.5.</span></p> </dd></dl> <dl class="function"> <dt id="codecs.getreader"> <tt class="descclassname">codecs.</tt><tt class="descname">getreader</tt><big>(</big><em>encoding</em><big>)</big><a class="headerlink" href="#codecs.getreader" title="Permalink to this definition">¶</a></dt> <dd><p>Look up the codec for the given encoding and return its StreamReader class or factory function.</p> <p>Raises a <a class="reference internal" href="exceptions.html#exceptions.LookupError" title="exceptions.LookupError"><tt class="xref py py-exc docutils literal"><span class="pre">LookupError</span></tt></a> in case the encoding cannot be found.</p> </dd></dl> <dl class="function"> <dt id="codecs.getwriter"> <tt class="descclassname">codecs.</tt><tt class="descname">getwriter</tt><big>(</big><em>encoding</em><big>)</big><a class="headerlink" href="#codecs.getwriter" title="Permalink to this definition">¶</a></dt> <dd><p>Look up the codec for the given encoding and return its StreamWriter class or factory function.</p> <p>Raises a <a class="reference internal" href="exceptions.html#exceptions.LookupError" title="exceptions.LookupError"><tt class="xref py py-exc docutils literal"><span class="pre">LookupError</span></tt></a> in case the encoding cannot be found.</p> </dd></dl> <dl class="function"> <dt id="codecs.register_error"> <tt class="descclassname">codecs.</tt><tt class="descname">register_error</tt><big>(</big><em>name</em>, <em>error_handler</em><big>)</big><a class="headerlink" href="#codecs.register_error" title="Permalink to this definition">¶</a></dt> <dd><p>Register the error handling function <em>error_handler</em> under the name <em>name</em>. <em>error_handler</em> will be called during encoding and decoding in case of an error, when <em>name</em> is specified as the errors parameter.</p> <p>For encoding <em>error_handler</em> will be called with a <a class="reference internal" href="exceptions.html#exceptions.UnicodeEncodeError" title="exceptions.UnicodeEncodeError"><tt class="xref py py-exc docutils literal"><span class="pre">UnicodeEncodeError</span></tt></a> instance, which contains information about the location of the error. The error handler must either raise this or a different exception or return a tuple with a replacement for the unencodable part of the input and a position where encoding should continue. The encoder will encode the replacement and continue encoding the original input at the specified position. Negative position values will be treated as being relative to the end of the input string. If the resulting position is out of bound an <a class="reference internal" href="exceptions.html#exceptions.IndexError" title="exceptions.IndexError"><tt class="xref py py-exc docutils literal"><span class="pre">IndexError</span></tt></a> will be raised.</p> <p>Decoding and translating works similar, except <a class="reference internal" href="exceptions.html#exceptions.UnicodeDecodeError" title="exceptions.UnicodeDecodeError"><tt class="xref py py-exc docutils literal"><span class="pre">UnicodeDecodeError</span></tt></a> or <a class="reference internal" href="exceptions.html#exceptions.UnicodeTranslateError" title="exceptions.UnicodeTranslateError"><tt class="xref py py-exc docutils literal"><span class="pre">UnicodeTranslateError</span></tt></a> will be passed to the handler and that the replacement from the error handler will be put into the output directly.</p> </dd></dl> <dl class="function"> <dt id="codecs.lookup_error"> <tt class="descclassname">codecs.</tt><tt class="descname">lookup_error</tt><big>(</big><em>name</em><big>)</big><a class="headerlink" href="#codecs.lookup_error" title="Permalink to this definition">¶</a></dt> <dd><p>Return the error handler previously registered under the name <em>name</em>.</p> <p>Raises a <a class="reference internal" href="exceptions.html#exceptions.LookupError" title="exceptions.LookupError"><tt class="xref py py-exc docutils literal"><span class="pre">LookupError</span></tt></a> in case the handler cannot be found.</p> </dd></dl> <dl class="function"> <dt id="codecs.strict_errors"> <tt class="descclassname">codecs.</tt><tt class="descname">strict_errors</tt><big>(</big><em>exception</em><big>)</big><a class="headerlink" href="#codecs.strict_errors" title="Permalink to this definition">¶</a></dt> <dd><p>Implements the <tt class="docutils literal"><span class="pre">strict</span></tt> error handling: each encoding or decoding error raises a <a class="reference internal" href="exceptions.html#exceptions.UnicodeError" title="exceptions.UnicodeError"><tt class="xref py py-exc docutils literal"><span class="pre">UnicodeError</span></tt></a>.</p> </dd></dl> <dl class="function"> <dt id="codecs.replace_errors"> <tt class="descclassname">codecs.</tt><tt class="descname">replace_errors</tt><big>(</big><em>exception</em><big>)</big><a class="headerlink" href="#codecs.replace_errors" title="Permalink to this definition">¶</a></dt> <dd><p>Implements the <tt class="docutils literal"><span class="pre">replace</span></tt> error handling: malformed data is replaced with a suitable replacement character such as <tt class="docutils literal"><span class="pre">'?'</span></tt> in bytestrings and <tt class="docutils literal"><span class="pre">'\ufffd'</span></tt> in Unicode strings.</p> </dd></dl> <dl class="function"> <dt id="codecs.ignore_errors"> <tt class="descclassname">codecs.</tt><tt class="descname">ignore_errors</tt><big>(</big><em>exception</em><big>)</big><a class="headerlink" href="#codecs.ignore_errors" title="Permalink to this definition">¶</a></dt> <dd><p>Implements the <tt class="docutils literal"><span class="pre">ignore</span></tt> error handling: malformed data is ignored and encoding or decoding is continued without further notice.</p> </dd></dl> <dl class="function"> <dt id="codecs.xmlcharrefreplace_errors"> <tt class="descclassname">codecs.</tt><tt class="descname">xmlcharrefreplace_errors</tt><big>(</big><em>exception</em><big>)</big><a class="headerlink" href="#codecs.xmlcharrefreplace_errors" title="Permalink to this definition">¶</a></dt> <dd><p>Implements the <tt class="docutils literal"><span class="pre">xmlcharrefreplace</span></tt> error handling (for encoding only): the unencodable character is replaced by an appropriate XML character reference.</p> </dd></dl> <dl class="function"> <dt id="codecs.backslashreplace_errors"> <tt class="descclassname">codecs.</tt><tt class="descname">backslashreplace_errors</tt><big>(</big><em>exception</em><big>)</big><a class="headerlink" href="#codecs.backslashreplace_errors" title="Permalink to this definition">¶</a></dt> <dd><p>Implements the <tt class="docutils literal"><span class="pre">backslashreplace</span></tt> error handling (for encoding only): the unencodable character is replaced by a backslashed escape sequence.</p> </dd></dl> <p>To simplify working with encoded files or stream, the module also defines these utility functions:</p> <dl class="function"> <dt id="codecs.open"> <tt class="descclassname">codecs.</tt><tt class="descname">open</tt><big>(</big><em>filename</em>, <em>mode</em><span class="optional">[</span>, <em>encoding</em><span class="optional">[</span>, <em>errors</em><span class="optional">[</span>, <em>buffering</em><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><big>)</big><a class="headerlink" href="#codecs.open" title="Permalink to this definition">¶</a></dt> <dd><p>Open an encoded file using the given <em>mode</em> and return a wrapped version providing transparent encoding/decoding. The default file mode is <tt class="docutils literal"><span class="pre">'r'</span></tt> meaning to open the file in read mode.</p> <div class="admonition note"> <p class="first admonition-title">Note</p> <p class="last">The wrapped version will only accept the object format defined by the codecs, i.e. Unicode objects for most built-in codecs. Output is also codec-dependent and will usually be Unicode as well.</p> </div> <div class="admonition note"> <p class="first admonition-title">Note</p> <p class="last">Files are always opened in binary mode, even if no binary mode was specified. This is done to avoid data loss due to encodings using 8-bit values. This means that no automatic conversion of <tt class="docutils literal"><span class="pre">'\n'</span></tt> is done on reading and writing.</p> </div> <p><em>encoding</em> specifies the encoding which is to be used for the file.</p> <p><em>errors</em> may be given to define the error handling. It defaults to <tt class="docutils literal"><span class="pre">'strict'</span></tt> which causes a <a class="reference internal" href="exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><tt class="xref py py-exc docutils literal"><span class="pre">ValueError</span></tt></a> to be raised in case an encoding error occurs.</p> <p><em>buffering</em> has the same meaning as for the built-in <a class="reference internal" href="functions.html#open" title="open"><tt class="xref py py-func docutils literal"><span class="pre">open()</span></tt></a> function. It defaults to line buffered.</p> </dd></dl> <dl class="function"> <dt id="codecs.EncodedFile"> <tt class="descclassname">codecs.</tt><tt class="descname">EncodedFile</tt><big>(</big><em>file</em>, <em>input</em><span class="optional">[</span>, <em>output</em><span class="optional">[</span>, <em>errors</em><span class="optional">]</span><span class="optional">]</span><big>)</big><a class="headerlink" href="#codecs.EncodedFile" title="Permalink to this definition">¶</a></dt> <dd><p>Return a wrapped version of file which provides transparent encoding translation.</p> <p>Strings written to the wrapped file are interpreted according to the given <em>input</em> encoding and then written to the original file as strings using the <em>output</em> encoding. The intermediate encoding will usually be Unicode but depends on the specified codecs.</p> <p>If <em>output</em> is not given, it defaults to <em>input</em>.</p> <p><em>errors</em> may be given to define the error handling. It defaults to <tt class="docutils literal"><span class="pre">'strict'</span></tt>, which causes <a class="reference internal" href="exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><tt class="xref py py-exc docutils literal"><span class="pre">ValueError</span></tt></a> to be raised in case an encoding error occurs.</p> </dd></dl> <dl class="function"> <dt id="codecs.iterencode"> <tt class="descclassname">codecs.</tt><tt class="descname">iterencode</tt><big>(</big><em>iterable</em>, <em>encoding</em><span class="optional">[</span>, <em>errors</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#codecs.iterencode" title="Permalink to this definition">¶</a></dt> <dd><p>Uses an incremental encoder to iteratively encode the input provided by <em>iterable</em>. This function is a <a class="reference internal" href="../glossary.html#term-generator"><em class="xref std std-term">generator</em></a>. <em>errors</em> (as well as any other keyword argument) is passed through to the incremental encoder.</p> <p class="versionadded"> <span class="versionmodified">New in version 2.5.</span></p> </dd></dl> <dl class="function"> <dt id="codecs.iterdecode"> <tt class="descclassname">codecs.</tt><tt class="descname">iterdecode</tt><big>(</big><em>iterable</em>, <em>encoding</em><span class="optional">[</span>, <em>errors</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#codecs.iterdecode" title="Permalink to this definition">¶</a></dt> <dd><p>Uses an incremental decoder to iteratively decode the input provided by <em>iterable</em>. This function is a <a class="reference internal" href="../glossary.html#term-generator"><em class="xref std std-term">generator</em></a>. <em>errors</em> (as well as any other keyword argument) is passed through to the incremental decoder.</p> <p class="versionadded"> <span class="versionmodified">New in version 2.5.</span></p> </dd></dl> <p>The module also provides the following constants which are useful for reading and writing to platform dependent files:</p> <dl class="data"> <dt id="codecs.BOM"> <tt class="descclassname">codecs.</tt><tt class="descname">BOM</tt><a class="headerlink" href="#codecs.BOM" title="Permalink to this definition">¶</a></dt> <dt id="codecs.BOM_BE"> <tt class="descclassname">codecs.</tt><tt class="descname">BOM_BE</tt><a class="headerlink" href="#codecs.BOM_BE" title="Permalink to this definition">¶</a></dt> <dt id="codecs.BOM_LE"> <tt class="descclassname">codecs.</tt><tt class="descname">BOM_LE</tt><a class="headerlink" href="#codecs.BOM_LE" title="Permalink to this definition">¶</a></dt> <dt id="codecs.BOM_UTF8"> <tt class="descclassname">codecs.</tt><tt class="descname">BOM_UTF8</tt><a class="headerlink" href="#codecs.BOM_UTF8" title="Permalink to this definition">¶</a></dt> <dt id="codecs.BOM_UTF16"> <tt class="descclassname">codecs.</tt><tt class="descname">BOM_UTF16</tt><a class="headerlink" href="#codecs.BOM_UTF16" title="Permalink to this definition">¶</a></dt> <dt id="codecs.BOM_UTF16_BE"> <tt class="descclassname">codecs.</tt><tt class="descname">BOM_UTF16_BE</tt><a class="headerlink" href="#codecs.BOM_UTF16_BE" title="Permalink to this definition">¶</a></dt> <dt id="codecs.BOM_UTF16_LE"> <tt class="descclassname">codecs.</tt><tt class="descname">BOM_UTF16_LE</tt><a class="headerlink" href="#codecs.BOM_UTF16_LE" title="Permalink to this definition">¶</a></dt> <dt id="codecs.BOM_UTF32"> <tt class="descclassname">codecs.</tt><tt class="descname">BOM_UTF32</tt><a class="headerlink" href="#codecs.BOM_UTF32" title="Permalink to this definition">¶</a></dt> <dt id="codecs.BOM_UTF32_BE"> <tt class="descclassname">codecs.</tt><tt class="descname">BOM_UTF32_BE</tt><a class="headerlink" href="#codecs.BOM_UTF32_BE" title="Permalink to this definition">¶</a></dt> <dt id="codecs.BOM_UTF32_LE"> <tt class="descclassname">codecs.</tt><tt class="descname">BOM_UTF32_LE</tt><a class="headerlink" href="#codecs.BOM_UTF32_LE" title="Permalink to this definition">¶</a></dt> <dd><p>These constants define various encodings of the Unicode byte order mark (BOM) used in UTF-16 and UTF-32 data streams to indicate the byte order used in the stream or file and in UTF-8 as a Unicode signature. <a class="reference internal" href="#codecs.BOM_UTF16" title="codecs.BOM_UTF16"><tt class="xref py py-const docutils literal"><span class="pre">BOM_UTF16</span></tt></a> is either <a class="reference internal" href="#codecs.BOM_UTF16_BE" title="codecs.BOM_UTF16_BE"><tt class="xref py py-const docutils literal"><span class="pre">BOM_UTF16_BE</span></tt></a> or <a class="reference internal" href="#codecs.BOM_UTF16_LE" title="codecs.BOM_UTF16_LE"><tt class="xref py py-const docutils literal"><span class="pre">BOM_UTF16_LE</span></tt></a> depending on the platform’s native byte order, <a class="reference internal" href="#codecs.BOM" title="codecs.BOM"><tt class="xref py py-const docutils literal"><span class="pre">BOM</span></tt></a> is an alias for <a class="reference internal" href="#codecs.BOM_UTF16" title="codecs.BOM_UTF16"><tt class="xref py py-const docutils literal"><span class="pre">BOM_UTF16</span></tt></a>, <a class="reference internal" href="#codecs.BOM_LE" title="codecs.BOM_LE"><tt class="xref py py-const docutils literal"><span class="pre">BOM_LE</span></tt></a> for <a class="reference internal" href="#codecs.BOM_UTF16_LE" title="codecs.BOM_UTF16_LE"><tt class="xref py py-const docutils literal"><span class="pre">BOM_UTF16_LE</span></tt></a> and <a class="reference internal" href="#codecs.BOM_BE" title="codecs.BOM_BE"><tt class="xref py py-const docutils literal"><span class="pre">BOM_BE</span></tt></a> for <a class="reference internal" href="#codecs.BOM_UTF16_BE" title="codecs.BOM_UTF16_BE"><tt class="xref py py-const docutils literal"><span class="pre">BOM_UTF16_BE</span></tt></a>. The others represent the BOM in UTF-8 and UTF-32 encodings.</p> </dd></dl> <div class="section" id="codec-base-classes"> <span id="id1"></span><h2>7.8.1. Codec Base Classes<a class="headerlink" href="#codec-base-classes" title="Permalink to this headline">¶</a></h2> <p>The <a class="reference internal" href="#module-codecs" title="codecs: Encode and decode data and streams."><tt class="xref py py-mod docutils literal"><span class="pre">codecs</span></tt></a> module defines a set of base classes which define the interface and can also be used to easily write your own codecs for use in Python.</p> <p>Each codec has to define four interfaces to make it usable as codec in Python: stateless encoder, stateless decoder, stream reader and stream writer. The stream reader and writers typically reuse the stateless encoder/decoder to implement the file protocols.</p> <p>The <tt class="xref py py-class docutils literal"><span class="pre">Codec</span></tt> class defines the interface for stateless encoders/decoders.</p> <p>To simplify and standardize error handling, the <tt class="xref py py-meth docutils literal"><span class="pre">encode()</span></tt> and <tt class="xref py py-meth docutils literal"><span class="pre">decode()</span></tt> methods may implement different error handling schemes by providing the <em>errors</em> string argument. The following string values are defined and implemented by all standard Python codecs:</p> <table border="1" class="docutils"> <colgroup> <col width="35%" /> <col width="65%" /> </colgroup> <thead valign="bottom"> <tr class="row-odd"><th class="head">Value</th> <th class="head">Meaning</th> </tr> </thead> <tbody valign="top"> <tr class="row-even"><td><tt class="docutils literal"><span class="pre">'strict'</span></tt></td> <td>Raise <a class="reference internal" href="exceptions.html#exceptions.UnicodeError" title="exceptions.UnicodeError"><tt class="xref py py-exc docutils literal"><span class="pre">UnicodeError</span></tt></a> (or a subclass); this is the default.</td> </tr> <tr class="row-odd"><td><tt class="docutils literal"><span class="pre">'ignore'</span></tt></td> <td>Ignore the character and continue with the next.</td> </tr> <tr class="row-even"><td><tt class="docutils literal"><span class="pre">'replace'</span></tt></td> <td>Replace with a suitable replacement character; Python will use the official U+FFFD REPLACEMENT CHARACTER for the built-in Unicode codecs on decoding and ‘?’ on encoding.</td> </tr> <tr class="row-odd"><td><tt class="docutils literal"><span class="pre">'xmlcharrefreplace'</span></tt></td> <td>Replace with the appropriate XML character reference (only for encoding).</td> </tr> <tr class="row-even"><td><tt class="docutils literal"><span class="pre">'backslashreplace'</span></tt></td> <td>Replace with backslashed escape sequences (only for encoding).</td> </tr> </tbody> </table> <p>The set of allowed values can be extended via <a class="reference internal" href="#codecs.register_error" title="codecs.register_error"><tt class="xref py py-meth docutils literal"><span class="pre">register_error()</span></tt></a>.</p> <div class="section" id="codec-objects"> <span id="id2"></span><h3>7.8.1.1. Codec Objects<a class="headerlink" href="#codec-objects" title="Permalink to this headline">¶</a></h3> <p>The <tt class="xref py py-class docutils literal"><span class="pre">Codec</span></tt> class defines these methods which also define the function interfaces of the stateless encoder and decoder:</p> <dl class="method"> <dt id="codecs.Codec.encode"> <tt class="descclassname">Codec.</tt><tt class="descname">encode</tt><big>(</big><em>input</em><span class="optional">[</span>, <em>errors</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#codecs.Codec.encode" title="Permalink to this definition">¶</a></dt> <dd><p>Encodes the object <em>input</em> and returns a tuple (output object, length consumed). While codecs are not restricted to use with Unicode, in a Unicode context, encoding converts a Unicode object to a plain string using a particular character set encoding (e.g., <tt class="docutils literal"><span class="pre">cp1252</span></tt> or <tt class="docutils literal"><span class="pre">iso-8859-1</span></tt>).</p> <p><em>errors</em> defines the error handling to apply. It defaults to <tt class="docutils literal"><span class="pre">'strict'</span></tt> handling.</p> <p>The method may not store state in the <tt class="xref py py-class docutils literal"><span class="pre">Codec</span></tt> instance. Use <tt class="xref py py-class docutils literal"><span class="pre">StreamCodec</span></tt> for codecs which have to keep state in order to make encoding/decoding efficient.</p> <p>The encoder must be able to handle zero length input and return an empty object of the output object type in this situation.</p> </dd></dl> <dl class="method"> <dt id="codecs.Codec.decode"> <tt class="descclassname">Codec.</tt><tt class="descname">decode</tt><big>(</big><em>input</em><span class="optional">[</span>, <em>errors</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#codecs.Codec.decode" title="Permalink to this definition">¶</a></dt> <dd><p>Decodes the object <em>input</em> and returns a tuple (output object, length consumed). In a Unicode context, decoding converts a plain string encoded using a particular character set encoding to a Unicode object.</p> <p><em>input</em> must be an object which provides the <tt class="docutils literal"><span class="pre">bf_getreadbuf</span></tt> buffer slot. Python strings, buffer objects and memory mapped files are examples of objects providing this slot.</p> <p><em>errors</em> defines the error handling to apply. It defaults to <tt class="docutils literal"><span class="pre">'strict'</span></tt> handling.</p> <p>The method may not store state in the <tt class="xref py py-class docutils literal"><span class="pre">Codec</span></tt> instance. Use <tt class="xref py py-class docutils literal"><span class="pre">StreamCodec</span></tt> for codecs which have to keep state in order to make encoding/decoding efficient.</p> <p>The decoder must be able to handle zero length input and return an empty object of the output object type in this situation.</p> </dd></dl> <p>The <a class="reference internal" href="#codecs.IncrementalEncoder" title="codecs.IncrementalEncoder"><tt class="xref py py-class docutils literal"><span class="pre">IncrementalEncoder</span></tt></a> and <a class="reference internal" href="#codecs.IncrementalDecoder" title="codecs.IncrementalDecoder"><tt class="xref py py-class docutils literal"><span class="pre">IncrementalDecoder</span></tt></a> classes provide the basic interface for incremental encoding and decoding. Encoding/decoding the input isn’t done with one call to the stateless encoder/decoder function, but with multiple calls to the <tt class="xref py py-meth docutils literal"><span class="pre">encode()</span></tt>/<tt class="xref py py-meth docutils literal"><span class="pre">decode()</span></tt> method of the incremental encoder/decoder. The incremental encoder/decoder keeps track of the encoding/decoding process during method calls.</p> <p>The joined output of calls to the <tt class="xref py py-meth docutils literal"><span class="pre">encode()</span></tt>/<tt class="xref py py-meth docutils literal"><span class="pre">decode()</span></tt> method is the same as if all the single inputs were joined into one, and this input was encoded/decoded with the stateless encoder/decoder.</p> </div> <div class="section" id="incrementalencoder-objects"> <span id="incremental-encoder-objects"></span><h3>7.8.1.2. IncrementalEncoder Objects<a class="headerlink" href="#incrementalencoder-objects" title="Permalink to this headline">¶</a></h3> <p class="versionadded"> <span class="versionmodified">New in version 2.5.</span></p> <p>The <a class="reference internal" href="#codecs.IncrementalEncoder" title="codecs.IncrementalEncoder"><tt class="xref py py-class docutils literal"><span class="pre">IncrementalEncoder</span></tt></a> class is used for encoding an input in multiple steps. It defines the following methods which every incremental encoder must define in order to be compatible with the Python codec registry.</p> <dl class="class"> <dt id="codecs.IncrementalEncoder"> <em class="property">class </em><tt class="descclassname">codecs.</tt><tt class="descname">IncrementalEncoder</tt><big>(</big><span class="optional">[</span><em>errors</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#codecs.IncrementalEncoder" title="Permalink to this definition">¶</a></dt> <dd><p>Constructor for an <a class="reference internal" href="#codecs.IncrementalEncoder" title="codecs.IncrementalEncoder"><tt class="xref py py-class docutils literal"><span class="pre">IncrementalEncoder</span></tt></a> instance.</p> <p>All incremental encoders must provide this constructor interface. They are free to add additional keyword arguments, but only the ones defined here are used by the Python codec registry.</p> <p>The <a class="reference internal" href="#codecs.IncrementalEncoder" title="codecs.IncrementalEncoder"><tt class="xref py py-class docutils literal"><span class="pre">IncrementalEncoder</span></tt></a> may implement different error handling schemes by providing the <em>errors</em> keyword argument. These parameters are predefined:</p> <ul class="simple"> <li><tt class="docutils literal"><span class="pre">'strict'</span></tt> Raise <a class="reference internal" href="exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><tt class="xref py py-exc docutils literal"><span class="pre">ValueError</span></tt></a> (or a subclass); this is the default.</li> <li><tt class="docutils literal"><span class="pre">'ignore'</span></tt> Ignore the character and continue with the next.</li> <li><tt class="docutils literal"><span class="pre">'replace'</span></tt> Replace with a suitable replacement character</li> <li><tt class="docutils literal"><span class="pre">'xmlcharrefreplace'</span></tt> Replace with the appropriate XML character reference</li> <li><tt class="docutils literal"><span class="pre">'backslashreplace'</span></tt> Replace with backslashed escape sequences.</li> </ul> <p>The <em>errors</em> argument will be assigned to an attribute of the same name. Assigning to this attribute makes it possible to switch between different error handling strategies during the lifetime of the <a class="reference internal" href="#codecs.IncrementalEncoder" title="codecs.IncrementalEncoder"><tt class="xref py py-class docutils literal"><span class="pre">IncrementalEncoder</span></tt></a> object.</p> <p>The set of allowed values for the <em>errors</em> argument can be extended with <a class="reference internal" href="#codecs.register_error" title="codecs.register_error"><tt class="xref py py-func docutils literal"><span class="pre">register_error()</span></tt></a>.</p> <dl class="method"> <dt id="codecs.IncrementalEncoder.encode"> <tt class="descname">encode</tt><big>(</big><em>object</em><span class="optional">[</span>, <em>final</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#codecs.IncrementalEncoder.encode" title="Permalink to this definition">¶</a></dt> <dd><p>Encodes <em>object</em> (taking the current state of the encoder into account) and returns the resulting encoded object. If this is the last call to <a class="reference internal" href="#codecs.IncrementalEncoder.encode" title="codecs.IncrementalEncoder.encode"><tt class="xref py py-meth docutils literal"><span class="pre">encode()</span></tt></a> <em>final</em> must be true (the default is false).</p> </dd></dl> <dl class="method"> <dt id="codecs.IncrementalEncoder.reset"> <tt class="descname">reset</tt><big>(</big><big>)</big><a class="headerlink" href="#codecs.IncrementalEncoder.reset" title="Permalink to this definition">¶</a></dt> <dd><p>Reset the encoder to the initial state.</p> </dd></dl> </dd></dl> </div> <div class="section" id="incrementaldecoder-objects"> <span id="incremental-decoder-objects"></span><h3>7.8.1.3. IncrementalDecoder Objects<a class="headerlink" href="#incrementaldecoder-objects" title="Permalink to this headline">¶</a></h3> <p>The <a class="reference internal" href="#codecs.IncrementalDecoder" title="codecs.IncrementalDecoder"><tt class="xref py py-class docutils literal"><span class="pre">IncrementalDecoder</span></tt></a> class is used for decoding an input in multiple steps. It defines the following methods which every incremental decoder must define in order to be compatible with the Python codec registry.</p> <dl class="class"> <dt id="codecs.IncrementalDecoder"> <em class="property">class </em><tt class="descclassname">codecs.</tt><tt class="descname">IncrementalDecoder</tt><big>(</big><span class="optional">[</span><em>errors</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#codecs.IncrementalDecoder" title="Permalink to this definition">¶</a></dt> <dd><p>Constructor for an <a class="reference internal" href="#codecs.IncrementalDecoder" title="codecs.IncrementalDecoder"><tt class="xref py py-class docutils literal"><span class="pre">IncrementalDecoder</span></tt></a> instance.</p> <p>All incremental decoders must provide this constructor interface. They are free to add additional keyword arguments, but only the ones defined here are used by the Python codec registry.</p> <p>The <a class="reference internal" href="#codecs.IncrementalDecoder" title="codecs.IncrementalDecoder"><tt class="xref py py-class docutils literal"><span class="pre">IncrementalDecoder</span></tt></a> may implement different error handling schemes by providing the <em>errors</em> keyword argument. These parameters are predefined:</p> <ul class="simple"> <li><tt class="docutils literal"><span class="pre">'strict'</span></tt> Raise <a class="reference internal" href="exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><tt class="xref py py-exc docutils literal"><span class="pre">ValueError</span></tt></a> (or a subclass); this is the default.</li> <li><tt class="docutils literal"><span class="pre">'ignore'</span></tt> Ignore the character and continue with the next.</li> <li><tt class="docutils literal"><span class="pre">'replace'</span></tt> Replace with a suitable replacement character.</li> </ul> <p>The <em>errors</em> argument will be assigned to an attribute of the same name. Assigning to this attribute makes it possible to switch between different error handling strategies during the lifetime of the <a class="reference internal" href="#codecs.IncrementalDecoder" title="codecs.IncrementalDecoder"><tt class="xref py py-class docutils literal"><span class="pre">IncrementalDecoder</span></tt></a> object.</p> <p>The set of allowed values for the <em>errors</em> argument can be extended with <a class="reference internal" href="#codecs.register_error" title="codecs.register_error"><tt class="xref py py-func docutils literal"><span class="pre">register_error()</span></tt></a>.</p> <dl class="method"> <dt id="codecs.IncrementalDecoder.decode"> <tt class="descname">decode</tt><big>(</big><em>object</em><span class="optional">[</span>, <em>final</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#codecs.IncrementalDecoder.decode" title="Permalink to this definition">¶</a></dt> <dd><p>Decodes <em>object</em> (taking the current state of the decoder into account) and returns the resulting decoded object. If this is the last call to <a class="reference internal" href="#codecs.IncrementalDecoder.decode" title="codecs.IncrementalDecoder.decode"><tt class="xref py py-meth docutils literal"><span class="pre">decode()</span></tt></a> <em>final</em> must be true (the default is false). If <em>final</em> is true the decoder must decode the input completely and must flush all buffers. If this isn’t possible (e.g. because of incomplete byte sequences at the end of the input) it must initiate error handling just like in the stateless case (which might raise an exception).</p> </dd></dl> <dl class="method"> <dt id="codecs.IncrementalDecoder.reset"> <tt class="descname">reset</tt><big>(</big><big>)</big><a class="headerlink" href="#codecs.IncrementalDecoder.reset" title="Permalink to this definition">¶</a></dt> <dd><p>Reset the decoder to the initial state.</p> </dd></dl> </dd></dl> <p>The <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><tt class="xref py py-class docutils literal"><span class="pre">StreamWriter</span></tt></a> and <a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><tt class="xref py py-class docutils literal"><span class="pre">StreamReader</span></tt></a> classes provide generic working interfaces which can be used to implement new encoding submodules very easily. See <tt class="xref py py-mod docutils literal"><span class="pre">encodings.utf_8</span></tt> for an example of how this is done.</p> </div> <div class="section" id="streamwriter-objects"> <span id="stream-writer-objects"></span><h3>7.8.1.4. StreamWriter Objects<a class="headerlink" href="#streamwriter-objects" title="Permalink to this headline">¶</a></h3> <p>The <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><tt class="xref py py-class docutils literal"><span class="pre">StreamWriter</span></tt></a> class is a subclass of <tt class="xref py py-class docutils literal"><span class="pre">Codec</span></tt> and defines the following methods which every stream writer must define in order to be compatible with the Python codec registry.</p> <dl class="class"> <dt id="codecs.StreamWriter"> <em class="property">class </em><tt class="descclassname">codecs.</tt><tt class="descname">StreamWriter</tt><big>(</big><em>stream</em><span class="optional">[</span>, <em>errors</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#codecs.StreamWriter" title="Permalink to this definition">¶</a></dt> <dd><p>Constructor for a <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><tt class="xref py py-class docutils literal"><span class="pre">StreamWriter</span></tt></a> instance.</p> <p>All stream writers must provide this constructor interface. They are free to add additional keyword arguments, but only the ones defined here are used by the Python codec registry.</p> <p><em>stream</em> must be a file-like object open for writing binary data.</p> <p>The <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><tt class="xref py py-class docutils literal"><span class="pre">StreamWriter</span></tt></a> may implement different error handling schemes by providing the <em>errors</em> keyword argument. These parameters are predefined:</p> <ul class="simple"> <li><tt class="docutils literal"><span class="pre">'strict'</span></tt> Raise <a class="reference internal" href="exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><tt class="xref py py-exc docutils literal"><span class="pre">ValueError</span></tt></a> (or a subclass); this is the default.</li> <li><tt class="docutils literal"><span class="pre">'ignore'</span></tt> Ignore the character and continue with the next.</li> <li><tt class="docutils literal"><span class="pre">'replace'</span></tt> Replace with a suitable replacement character</li> <li><tt class="docutils literal"><span class="pre">'xmlcharrefreplace'</span></tt> Replace with the appropriate XML character reference</li> <li><tt class="docutils literal"><span class="pre">'backslashreplace'</span></tt> Replace with backslashed escape sequences.</li> </ul> <p>The <em>errors</em> argument will be assigned to an attribute of the same name. Assigning to this attribute makes it possible to switch between different error handling strategies during the lifetime of the <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><tt class="xref py py-class docutils literal"><span class="pre">StreamWriter</span></tt></a> object.</p> <p>The set of allowed values for the <em>errors</em> argument can be extended with <a class="reference internal" href="#codecs.register_error" title="codecs.register_error"><tt class="xref py py-func docutils literal"><span class="pre">register_error()</span></tt></a>.</p> <dl class="method"> <dt id="codecs.StreamWriter.write"> <tt class="descname">write</tt><big>(</big><em>object</em><big>)</big><a class="headerlink" href="#codecs.StreamWriter.write" title="Permalink to this definition">¶</a></dt> <dd><p>Writes the object’s contents encoded to the stream.</p> </dd></dl> <dl class="method"> <dt id="codecs.StreamWriter.writelines"> <tt class="descname">writelines</tt><big>(</big><em>list</em><big>)</big><a class="headerlink" href="#codecs.StreamWriter.writelines" title="Permalink to this definition">¶</a></dt> <dd><p>Writes the concatenated list of strings to the stream (possibly by reusing the <a class="reference internal" href="#codecs.StreamWriter.write" title="codecs.StreamWriter.write"><tt class="xref py py-meth docutils literal"><span class="pre">write()</span></tt></a> method).</p> </dd></dl> <dl class="method"> <dt id="codecs.StreamWriter.reset"> <tt class="descname">reset</tt><big>(</big><big>)</big><a class="headerlink" href="#codecs.StreamWriter.reset" title="Permalink to this definition">¶</a></dt> <dd><p>Flushes and resets the codec buffers used for keeping state.</p> <p>Calling this method should ensure that the data on the output is put into a clean state that allows appending of new fresh data without having to rescan the whole stream to recover state.</p> </dd></dl> </dd></dl> <p>In addition to the above methods, the <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><tt class="xref py py-class docutils literal"><span class="pre">StreamWriter</span></tt></a> must also inherit all other methods and attributes from the underlying stream.</p> </div> <div class="section" id="streamreader-objects"> <span id="stream-reader-objects"></span><h3>7.8.1.5. StreamReader Objects<a class="headerlink" href="#streamreader-objects" title="Permalink to this headline">¶</a></h3> <p>The <a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><tt class="xref py py-class docutils literal"><span class="pre">StreamReader</span></tt></a> class is a subclass of <tt class="xref py py-class docutils literal"><span class="pre">Codec</span></tt> and defines the following methods which every stream reader must define in order to be compatible with the Python codec registry.</p> <dl class="class"> <dt id="codecs.StreamReader"> <em class="property">class </em><tt class="descclassname">codecs.</tt><tt class="descname">StreamReader</tt><big>(</big><em>stream</em><span class="optional">[</span>, <em>errors</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#codecs.StreamReader" title="Permalink to this definition">¶</a></dt> <dd><p>Constructor for a <a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><tt class="xref py py-class docutils literal"><span class="pre">StreamReader</span></tt></a> instance.</p> <p>All stream readers must provide this constructor interface. They are free to add additional keyword arguments, but only the ones defined here are used by the Python codec registry.</p> <p><em>stream</em> must be a file-like object open for reading (binary) data.</p> <p>The <a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><tt class="xref py py-class docutils literal"><span class="pre">StreamReader</span></tt></a> may implement different error handling schemes by providing the <em>errors</em> keyword argument. These parameters are defined:</p> <ul class="simple"> <li><tt class="docutils literal"><span class="pre">'strict'</span></tt> Raise <a class="reference internal" href="exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><tt class="xref py py-exc docutils literal"><span class="pre">ValueError</span></tt></a> (or a subclass); this is the default.</li> <li><tt class="docutils literal"><span class="pre">'ignore'</span></tt> Ignore the character and continue with the next.</li> <li><tt class="docutils literal"><span class="pre">'replace'</span></tt> Replace with a suitable replacement character.</li> </ul> <p>The <em>errors</em> argument will be assigned to an attribute of the same name. Assigning to this attribute makes it possible to switch between different error handling strategies during the lifetime of the <a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><tt class="xref py py-class docutils literal"><span class="pre">StreamReader</span></tt></a> object.</p> <p>The set of allowed values for the <em>errors</em> argument can be extended with <a class="reference internal" href="#codecs.register_error" title="codecs.register_error"><tt class="xref py py-func docutils literal"><span class="pre">register_error()</span></tt></a>.</p> <dl class="method"> <dt id="codecs.StreamReader.read"> <tt class="descname">read</tt><big>(</big><span class="optional">[</span><em>size</em><span class="optional">[</span>, <em>chars</em><span class="optional">[</span>, <em>firstline</em><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><big>)</big><a class="headerlink" href="#codecs.StreamReader.read" title="Permalink to this definition">¶</a></dt> <dd><p>Decodes data from the stream and returns the resulting object.</p> <p><em>chars</em> indicates the number of characters to read from the stream. <a class="reference internal" href="#codecs.StreamReader.read" title="codecs.StreamReader.read"><tt class="xref py py-func docutils literal"><span class="pre">read()</span></tt></a> will never return more than <em>chars</em> characters, but it might return less, if there are not enough characters available.</p> <p><em>size</em> indicates the approximate maximum number of bytes to read from the stream for decoding purposes. The decoder can modify this setting as appropriate. The default value -1 indicates to read and decode as much as possible. <em>size</em> is intended to prevent having to decode huge files in one step.</p> <p><em>firstline</em> indicates that it would be sufficient to only return the first line, if there are decoding errors on later lines.</p> <p>The method should use a greedy read strategy meaning that it should read as much data as is allowed within the definition of the encoding and the given size, e.g. if optional encoding endings or state markers are available on the stream, these should be read too.</p> <p class="versionchanged"> <span class="versionmodified">Changed in version 2.4: </span><em>chars</em> argument added.</p> <p class="versionchanged"> <span class="versionmodified">Changed in version 2.4.2: </span><em>firstline</em> argument added.</p> </dd></dl> <dl class="method"> <dt id="codecs.StreamReader.readline"> <tt class="descname">readline</tt><big>(</big><span class="optional">[</span><em>size</em><span class="optional">[</span>, <em>keepends</em><span class="optional">]</span><span class="optional">]</span><big>)</big><a class="headerlink" href="#codecs.StreamReader.readline" title="Permalink to this definition">¶</a></dt> <dd><p>Read one line from the input stream and return the decoded data.</p> <p><em>size</em>, if given, is passed as size argument to the stream’s <a class="reference internal" href="readline.html#module-readline" title="readline: GNU readline support for Python. (Unix)"><tt class="xref py py-meth docutils literal"><span class="pre">readline()</span></tt></a> method.</p> <p>If <em>keepends</em> is false line-endings will be stripped from the lines returned.</p> <p class="versionchanged"> <span class="versionmodified">Changed in version 2.4: </span><em>keepends</em> argument added.</p> </dd></dl> <dl class="method"> <dt id="codecs.StreamReader.readlines"> <tt class="descname">readlines</tt><big>(</big><span class="optional">[</span><em>sizehint</em><span class="optional">[</span>, <em>keepends</em><span class="optional">]</span><span class="optional">]</span><big>)</big><a class="headerlink" href="#codecs.StreamReader.readlines" title="Permalink to this definition">¶</a></dt> <dd><p>Read all lines available on the input stream and return them as a list of lines.</p> <p>Line-endings are implemented using the codec’s decoder method and are included in the list entries if <em>keepends</em> is true.</p> <p><em>sizehint</em>, if given, is passed as the <em>size</em> argument to the stream’s <a class="reference internal" href="#codecs.StreamReader.read" title="codecs.StreamReader.read"><tt class="xref py py-meth docutils literal"><span class="pre">read()</span></tt></a> method.</p> </dd></dl> <dl class="method"> <dt id="codecs.StreamReader.reset"> <tt class="descname">reset</tt><big>(</big><big>)</big><a class="headerlink" href="#codecs.StreamReader.reset" title="Permalink to this definition">¶</a></dt> <dd><p>Resets the codec buffers used for keeping state.</p> <p>Note that no stream repositioning should take place. This method is primarily intended to be able to recover from decoding errors.</p> </dd></dl> </dd></dl> <p>In addition to the above methods, the <a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><tt class="xref py py-class docutils literal"><span class="pre">StreamReader</span></tt></a> must also inherit all other methods and attributes from the underlying stream.</p> <p>The next two base classes are included for convenience. They are not needed by the codec registry, but may provide useful in practice.</p> </div> <div class="section" id="streamreaderwriter-objects"> <span id="stream-reader-writer"></span><h3>7.8.1.6. StreamReaderWriter Objects<a class="headerlink" href="#streamreaderwriter-objects" title="Permalink to this headline">¶</a></h3> <p>The <a class="reference internal" href="#codecs.StreamReaderWriter" title="codecs.StreamReaderWriter"><tt class="xref py py-class docutils literal"><span class="pre">StreamReaderWriter</span></tt></a> allows wrapping streams which work in both read and write modes.</p> <p>The design is such that one can use the factory functions returned by the <a class="reference internal" href="#codecs.lookup" title="codecs.lookup"><tt class="xref py py-func docutils literal"><span class="pre">lookup()</span></tt></a> function to construct the instance.</p> <dl class="class"> <dt id="codecs.StreamReaderWriter"> <em class="property">class </em><tt class="descclassname">codecs.</tt><tt class="descname">StreamReaderWriter</tt><big>(</big><em>stream</em>, <em>Reader</em>, <em>Writer</em>, <em>errors</em><big>)</big><a class="headerlink" href="#codecs.StreamReaderWriter" title="Permalink to this definition">¶</a></dt> <dd><p>Creates a <a class="reference internal" href="#codecs.StreamReaderWriter" title="codecs.StreamReaderWriter"><tt class="xref py py-class docutils literal"><span class="pre">StreamReaderWriter</span></tt></a> instance. <em>stream</em> must be a file-like object. <em>Reader</em> and <em>Writer</em> must be factory functions or classes providing the <a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><tt class="xref py py-class docutils literal"><span class="pre">StreamReader</span></tt></a> and <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><tt class="xref py py-class docutils literal"><span class="pre">StreamWriter</span></tt></a> interface resp. Error handling is done in the same way as defined for the stream readers and writers.</p> </dd></dl> <p><a class="reference internal" href="#codecs.StreamReaderWriter" title="codecs.StreamReaderWriter"><tt class="xref py py-class docutils literal"><span class="pre">StreamReaderWriter</span></tt></a> instances define the combined interfaces of <a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><tt class="xref py py-class docutils literal"><span class="pre">StreamReader</span></tt></a> and <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><tt class="xref py py-class docutils literal"><span class="pre">StreamWriter</span></tt></a> classes. They inherit all other methods and attributes from the underlying stream.</p> </div> <div class="section" id="streamrecoder-objects"> <span id="stream-recoder-objects"></span><h3>7.8.1.7. StreamRecoder Objects<a class="headerlink" href="#streamrecoder-objects" title="Permalink to this headline">¶</a></h3> <p>The <a class="reference internal" href="#codecs.StreamRecoder" title="codecs.StreamRecoder"><tt class="xref py py-class docutils literal"><span class="pre">StreamRecoder</span></tt></a> provide a frontend - backend view of encoding data which is sometimes useful when dealing with different encoding environments.</p> <p>The design is such that one can use the factory functions returned by the <a class="reference internal" href="#codecs.lookup" title="codecs.lookup"><tt class="xref py py-func docutils literal"><span class="pre">lookup()</span></tt></a> function to construct the instance.</p> <dl class="class"> <dt id="codecs.StreamRecoder"> <em class="property">class </em><tt class="descclassname">codecs.</tt><tt class="descname">StreamRecoder</tt><big>(</big><em>stream</em>, <em>encode</em>, <em>decode</em>, <em>Reader</em>, <em>Writer</em>, <em>errors</em><big>)</big><a class="headerlink" href="#codecs.StreamRecoder" title="Permalink to this definition">¶</a></dt> <dd><p>Creates a <a class="reference internal" href="#codecs.StreamRecoder" title="codecs.StreamRecoder"><tt class="xref py py-class docutils literal"><span class="pre">StreamRecoder</span></tt></a> instance which implements a two-way conversion: <em>encode</em> and <em>decode</em> work on the frontend (the input to <tt class="xref py py-meth docutils literal"><span class="pre">read()</span></tt> and output of <tt class="xref py py-meth docutils literal"><span class="pre">write()</span></tt>) while <em>Reader</em> and <em>Writer</em> work on the backend (reading and writing to the stream).</p> <p>You can use these objects to do transparent direct recodings from e.g. Latin-1 to UTF-8 and back.</p> <p><em>stream</em> must be a file-like object.</p> <p><em>encode</em>, <em>decode</em> must adhere to the <tt class="xref py py-class docutils literal"><span class="pre">Codec</span></tt> interface. <em>Reader</em>, <em>Writer</em> must be factory functions or classes providing objects of the <a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><tt class="xref py py-class docutils literal"><span class="pre">StreamReader</span></tt></a> and <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><tt class="xref py py-class docutils literal"><span class="pre">StreamWriter</span></tt></a> interface respectively.</p> <p><em>encode</em> and <em>decode</em> are needed for the frontend translation, <em>Reader</em> and <em>Writer</em> for the backend translation. The intermediate format used is determined by the two sets of codecs, e.g. the Unicode codecs will use Unicode as the intermediate encoding.</p> <p>Error handling is done in the same way as defined for the stream readers and writers.</p> </dd></dl> <p><a class="reference internal" href="#codecs.StreamRecoder" title="codecs.StreamRecoder"><tt class="xref py py-class docutils literal"><span class="pre">StreamRecoder</span></tt></a> instances define the combined interfaces of <a class="reference internal" href="#codecs.StreamReader" title="codecs.StreamReader"><tt class="xref py py-class docutils literal"><span class="pre">StreamReader</span></tt></a> and <a class="reference internal" href="#codecs.StreamWriter" title="codecs.StreamWriter"><tt class="xref py py-class docutils literal"><span class="pre">StreamWriter</span></tt></a> classes. They inherit all other methods and attributes from the underlying stream.</p> </div> </div> <div class="section" id="encodings-and-unicode"> <span id="encodings-overview"></span><h2>7.8.2. Encodings and Unicode<a class="headerlink" href="#encodings-and-unicode" title="Permalink to this headline">¶</a></h2> <p>Unicode strings are stored internally as sequences of codepoints (to be precise as <a class="reference internal" href="../c-api/unicode.html#Py_UNICODE" title="Py_UNICODE"><tt class="xref c c-type docutils literal"><span class="pre">Py_UNICODE</span></tt></a> arrays). Depending on the way Python is compiled (either via <tt class="docutils literal"><span class="pre">--enable-unicode=ucs2</span></tt> or <tt class="docutils literal"><span class="pre">--enable-unicode=ucs4</span></tt>, with the former being the default) <a class="reference internal" href="../c-api/unicode.html#Py_UNICODE" title="Py_UNICODE"><tt class="xref c c-type docutils literal"><span class="pre">Py_UNICODE</span></tt></a> is either a 16-bit or 32-bit data type. Once a Unicode object is used outside of CPU and memory, CPU endianness and how these arrays are stored as bytes become an issue. Transforming a unicode object into a sequence of bytes is called encoding and recreating the unicode object from the sequence of bytes is known as decoding. There are many different methods for how this transformation can be done (these methods are also called encodings). The simplest method is to map the codepoints 0-255 to the bytes <tt class="docutils literal"><span class="pre">0x0</span></tt>-<tt class="docutils literal"><span class="pre">0xff</span></tt>. This means that a unicode object that contains codepoints above <tt class="docutils literal"><span class="pre">U+00FF</span></tt> can’t be encoded with this method (which is called <tt class="docutils literal"><span class="pre">'latin-1'</span></tt> or <tt class="docutils literal"><span class="pre">'iso-8859-1'</span></tt>). <tt class="xref py py-func docutils literal"><span class="pre">unicode.encode()</span></tt> will raise a <a class="reference internal" href="exceptions.html#exceptions.UnicodeEncodeError" title="exceptions.UnicodeEncodeError"><tt class="xref py py-exc docutils literal"><span class="pre">UnicodeEncodeError</span></tt></a> that looks like this: <tt class="docutils literal"><span class="pre">UnicodeEncodeError:</span> <span class="pre">'latin-1'</span> <span class="pre">codec</span> <span class="pre">can't</span> <span class="pre">encode</span> <span class="pre">character</span> <span class="pre">u'\u1234'</span> <span class="pre">in</span> <span class="pre">position</span> <span class="pre">3:</span> <span class="pre">ordinal</span> <span class="pre">not</span> <span class="pre">in</span> <span class="pre">range(256)</span></tt>.</p> <p>There’s another group of encodings (the so called charmap encodings) that choose a different subset of all unicode code points and how these codepoints are mapped to the bytes <tt class="docutils literal"><span class="pre">0x0</span></tt>-<tt class="docutils literal"><span class="pre">0xff</span></tt>. To see how this is done simply open e.g. <tt class="file docutils literal"><span class="pre">encodings/cp1252.py</span></tt> (which is an encoding that is used primarily on Windows). There’s a string constant with 256 characters that shows you which character is mapped to which byte value.</p> <p>All of these encodings can only encode 256 of the 1114112 codepoints defined in unicode. A simple and straightforward way that can store each Unicode code point, is to store each codepoint as four consecutive bytes. There are two possibilities: store the bytes in big endian or in little endian order. These two encodings are called <tt class="docutils literal"><span class="pre">UTF-32-BE</span></tt> and <tt class="docutils literal"><span class="pre">UTF-32-LE</span></tt> respectively. Their disadvantage is that if e.g. you use <tt class="docutils literal"><span class="pre">UTF-32-BE</span></tt> on a little endian machine you will always have to swap bytes on encoding and decoding. <tt class="docutils literal"><span class="pre">UTF-32</span></tt> avoids this problem: bytes will always be in natural endianness. When these bytes are read by a CPU with a different endianness, then bytes have to be swapped though. To be able to detect the endianness of a <tt class="docutils literal"><span class="pre">UTF-16</span></tt> or <tt class="docutils literal"><span class="pre">UTF-32</span></tt> byte sequence, there’s the so called BOM (“Byte Order Mark”). This is the Unicode character <tt class="docutils literal"><span class="pre">U+FEFF</span></tt>. This character can be prepended to every <tt class="docutils literal"><span class="pre">UTF-16</span></tt> or <tt class="docutils literal"><span class="pre">UTF-32</span></tt> byte sequence. The byte swapped version of this character (<tt class="docutils literal"><span class="pre">0xFFFE</span></tt>) is an illegal character that may not appear in a Unicode text. So when the first character in an <tt class="docutils literal"><span class="pre">UTF-16</span></tt> or <tt class="docutils literal"><span class="pre">UTF-32</span></tt> byte sequence appears to be a <tt class="docutils literal"><span class="pre">U+FFFE</span></tt> the bytes have to be swapped on decoding. Unfortunately the character <tt class="docutils literal"><span class="pre">U+FEFF</span></tt> had a second purpose as a <tt class="docutils literal"><span class="pre">ZERO</span> <span class="pre">WIDTH</span> <span class="pre">NO-BREAK</span> <span class="pre">SPACE</span></tt>: a character that has no width and doesn’t allow a word to be split. It can e.g. be used to give hints to a ligature algorithm. With Unicode 4.0 using <tt class="docutils literal"><span class="pre">U+FEFF</span></tt> as a <tt class="docutils literal"><span class="pre">ZERO</span> <span class="pre">WIDTH</span> <span class="pre">NO-BREAK</span> <span class="pre">SPACE</span></tt> has been deprecated (with <tt class="docutils literal"><span class="pre">U+2060</span></tt> (<tt class="docutils literal"><span class="pre">WORD</span> <span class="pre">JOINER</span></tt>) assuming this role). Nevertheless Unicode software still must be able to handle <tt class="docutils literal"><span class="pre">U+FEFF</span></tt> in both roles: as a BOM it’s a device to determine the storage layout of the encoded bytes, and vanishes once the byte sequence has been decoded into a Unicode string; as a <tt class="docutils literal"><span class="pre">ZERO</span> <span class="pre">WIDTH</span> <span class="pre">NO-BREAK</span> <span class="pre">SPACE</span></tt> it’s a normal character that will be decoded like any other.</p> <p>There’s another encoding that is able to encoding the full range of Unicode characters: UTF-8. UTF-8 is an 8-bit encoding, which means there are no issues with byte order in UTF-8. Each byte in a UTF-8 byte sequence consists of two parts: marker bits (the most significant bits) and payload bits. The marker bits are a sequence of zero to four <tt class="docutils literal"><span class="pre">1</span></tt> bits followed by a <tt class="docutils literal"><span class="pre">0</span></tt> bit. Unicode characters are encoded like this (with x being payload bits, which when concatenated give the Unicode character):</p> <table border="1" class="docutils"> <colgroup> <col width="43%" /> <col width="57%" /> </colgroup> <thead valign="bottom"> <tr class="row-odd"><th class="head">Range</th> <th class="head">Encoding</th> </tr> </thead> <tbody valign="top"> <tr class="row-even"><td><tt class="docutils literal"><span class="pre">U-00000000</span></tt> ... <tt class="docutils literal"><span class="pre">U-0000007F</span></tt></td> <td>0xxxxxxx</td> </tr> <tr class="row-odd"><td><tt class="docutils literal"><span class="pre">U-00000080</span></tt> ... <tt class="docutils literal"><span class="pre">U-000007FF</span></tt></td> <td>110xxxxx 10xxxxxx</td> </tr> <tr class="row-even"><td><tt class="docutils literal"><span class="pre">U-00000800</span></tt> ... <tt class="docutils literal"><span class="pre">U-0000FFFF</span></tt></td> <td>1110xxxx 10xxxxxx 10xxxxxx</td> </tr> <tr class="row-odd"><td><tt class="docutils literal"><span class="pre">U-00010000</span></tt> ... <tt class="docutils literal"><span class="pre">U-0010FFFF</span></tt></td> <td>11110xxx 10xxxxxx 10xxxxxx 10xxxxxx</td> </tr> </tbody> </table> <p>The least significant bit of the Unicode character is the rightmost x bit.</p> <p>As UTF-8 is an 8-bit encoding no BOM is required and any <tt class="docutils literal"><span class="pre">U+FEFF</span></tt> character in the decoded Unicode string (even if it’s the first character) is treated as a <tt class="docutils literal"><span class="pre">ZERO</span> <span class="pre">WIDTH</span> <span class="pre">NO-BREAK</span> <span class="pre">SPACE</span></tt>.</p> <p>Without external information it’s impossible to reliably determine which encoding was used for encoding a Unicode string. Each charmap encoding can decode any random byte sequence. However that’s not possible with UTF-8, as UTF-8 byte sequences have a structure that doesn’t allow arbitrary byte sequences. To increase the reliability with which a UTF-8 encoding can be detected, Microsoft invented a variant of UTF-8 (that Python 2.5 calls <tt class="docutils literal"><span class="pre">"utf-8-sig"</span></tt>) for its Notepad program: Before any of the Unicode characters is written to the file, a UTF-8 encoded BOM (which looks like this as a byte sequence: <tt class="docutils literal"><span class="pre">0xef</span></tt>, <tt class="docutils literal"><span class="pre">0xbb</span></tt>, <tt class="docutils literal"><span class="pre">0xbf</span></tt>) is written. As it’s rather improbable that any charmap encoded file starts with these byte values (which would e.g. map to</p> <blockquote> <div><div class="line-block"> <div class="line">LATIN SMALL LETTER I WITH DIAERESIS</div> <div class="line">RIGHT-POINTING DOUBLE ANGLE QUOTATION MARK</div> <div class="line">INVERTED QUESTION MARK</div> </div> </div></blockquote> <p>in iso-8859-1), this increases the probability that a <tt class="docutils literal"><span class="pre">utf-8-sig</span></tt> encoding can be correctly guessed from the byte sequence. So here the BOM is not used to be able to determine the byte order used for generating the byte sequence, but as a signature that helps in guessing the encoding. On encoding the utf-8-sig codec will write <tt class="docutils literal"><span class="pre">0xef</span></tt>, <tt class="docutils literal"><span class="pre">0xbb</span></tt>, <tt class="docutils literal"><span class="pre">0xbf</span></tt> as the first three bytes to the file. On decoding <tt class="docutils literal"><span class="pre">utf-8-sig</span></tt> will skip those three bytes if they appear as the first three bytes in the file. In UTF-8, the use of the BOM is discouraged and should generally be avoided.</p> </div> <div class="section" id="standard-encodings"> <span id="id3"></span><h2>7.8.3. Standard Encodings<a class="headerlink" href="#standard-encodings" title="Permalink to this headline">¶</a></h2> <p>Python comes with a number of codecs built-in, either implemented as C functions or with dictionaries as mapping tables. The following table lists the codecs by name, together with a few common aliases, and the languages for which the encoding is likely used. Neither the list of aliases nor the list of languages is meant to be exhaustive. Notice that spelling alternatives that only differ in case or use a hyphen instead of an underscore are also valid aliases; therefore, e.g. <tt class="docutils literal"><span class="pre">'utf-8'</span></tt> is a valid alias for the <tt class="docutils literal"><span class="pre">'utf_8'</span></tt> codec.</p> <p>Many of the character sets support the same languages. They vary in individual characters (e.g. whether the EURO SIGN is supported or not), and in the assignment of characters to code positions. For the European languages in particular, the following variants typically exist:</p> <ul class="simple"> <li>an ISO 8859 codeset</li> <li>a Microsoft Windows code page, which is typically derived from a 8859 codeset, but replaces control characters with additional graphic characters</li> <li>an IBM EBCDIC code page</li> <li>an IBM PC code page, which is ASCII compatible</li> </ul> <table border="1" class="docutils"> <colgroup> <col width="21%" /> <col width="40%" /> <col width="40%" /> </colgroup> <thead valign="bottom"> <tr class="row-odd"><th class="head">Codec</th> <th class="head">Aliases</th> <th class="head">Languages</th> </tr> </thead> <tbody valign="top"> <tr class="row-even"><td>ascii</td> <td>646, us-ascii</td> <td>English</td> </tr> <tr class="row-odd"><td>big5</td> <td>big5-tw, csbig5</td> <td>Traditional Chinese</td> </tr> <tr class="row-even"><td>big5hkscs</td> <td>big5-hkscs, hkscs</td> <td>Traditional Chinese</td> </tr> <tr class="row-odd"><td>cp037</td> <td>IBM037, IBM039</td> <td>English</td> </tr> <tr class="row-even"><td>cp424</td> <td>EBCDIC-CP-HE, IBM424</td> <td>Hebrew</td> </tr> <tr class="row-odd"><td>cp437</td> <td>437, IBM437</td> <td>English</td> </tr> <tr class="row-even"><td>cp500</td> <td>EBCDIC-CP-BE, EBCDIC-CP-CH, IBM500</td> <td>Western Europe</td> </tr> <tr class="row-odd"><td>cp720</td> <td> </td> <td>Arabic</td> </tr> <tr class="row-even"><td>cp737</td> <td> </td> <td>Greek</td> </tr> <tr class="row-odd"><td>cp775</td> <td>IBM775</td> <td>Baltic languages</td> </tr> <tr class="row-even"><td>cp850</td> <td>850, IBM850</td> <td>Western Europe</td> </tr> <tr class="row-odd"><td>cp852</td> <td>852, IBM852</td> <td>Central and Eastern Europe</td> </tr> <tr class="row-even"><td>cp855</td> <td>855, IBM855</td> <td>Bulgarian, Byelorussian, Macedonian, Russian, Serbian</td> </tr> <tr class="row-odd"><td>cp856</td> <td> </td> <td>Hebrew</td> </tr> <tr class="row-even"><td>cp857</td> <td>857, IBM857</td> <td>Turkish</td> </tr> <tr class="row-odd"><td>cp858</td> <td>858, IBM858</td> <td>Western Europe</td> </tr> <tr class="row-even"><td>cp860</td> <td>860, IBM860</td> <td>Portuguese</td> </tr> <tr class="row-odd"><td>cp861</td> <td>861, CP-IS, IBM861</td> <td>Icelandic</td> </tr> <tr class="row-even"><td>cp862</td> <td>862, IBM862</td> <td>Hebrew</td> </tr> <tr class="row-odd"><td>cp863</td> <td>863, IBM863</td> <td>Canadian</td> </tr> <tr class="row-even"><td>cp864</td> <td>IBM864</td> <td>Arabic</td> </tr> <tr class="row-odd"><td>cp865</td> <td>865, IBM865</td> <td>Danish, Norwegian</td> </tr> <tr class="row-even"><td>cp866</td> <td>866, IBM866</td> <td>Russian</td> </tr> <tr class="row-odd"><td>cp869</td> <td>869, CP-GR, IBM869</td> <td>Greek</td> </tr> <tr class="row-even"><td>cp874</td> <td> </td> <td>Thai</td> </tr> <tr class="row-odd"><td>cp875</td> <td> </td> <td>Greek</td> </tr> <tr class="row-even"><td>cp932</td> <td>932, ms932, mskanji, ms-kanji</td> <td>Japanese</td> </tr> <tr class="row-odd"><td>cp949</td> <td>949, ms949, uhc</td> <td>Korean</td> </tr> <tr class="row-even"><td>cp950</td> <td>950, ms950</td> <td>Traditional Chinese</td> </tr> <tr class="row-odd"><td>cp1006</td> <td> </td> <td>Urdu</td> </tr> <tr class="row-even"><td>cp1026</td> <td>ibm1026</td> <td>Turkish</td> </tr> <tr class="row-odd"><td>cp1140</td> <td>ibm1140</td> <td>Western Europe</td> </tr> <tr class="row-even"><td>cp1250</td> <td>windows-1250</td> <td>Central and Eastern Europe</td> </tr> <tr class="row-odd"><td>cp1251</td> <td>windows-1251</td> <td>Bulgarian, Byelorussian, Macedonian, Russian, Serbian</td> </tr> <tr class="row-even"><td>cp1252</td> <td>windows-1252</td> <td>Western Europe</td> </tr> <tr class="row-odd"><td>cp1253</td> <td>windows-1253</td> <td>Greek</td> </tr> <tr class="row-even"><td>cp1254</td> <td>windows-1254</td> <td>Turkish</td> </tr> <tr class="row-odd"><td>cp1255</td> <td>windows-1255</td> <td>Hebrew</td> </tr> <tr class="row-even"><td>cp1256</td> <td>windows-1256</td> <td>Arabic</td> </tr> <tr class="row-odd"><td>cp1257</td> <td>windows-1257</td> <td>Baltic languages</td> </tr> <tr class="row-even"><td>cp1258</td> <td>windows-1258</td> <td>Vietnamese</td> </tr> <tr class="row-odd"><td>euc_jp</td> <td>eucjp, ujis, u-jis</td> <td>Japanese</td> </tr> <tr class="row-even"><td>euc_jis_2004</td> <td>jisx0213, eucjis2004</td> <td>Japanese</td> </tr> <tr class="row-odd"><td>euc_jisx0213</td> <td>eucjisx0213</td> <td>Japanese</td> </tr> <tr class="row-even"><td>euc_kr</td> <td>euckr, korean, ksc5601, ks_c-5601, ks_c-5601-1987, ksx1001, ks_x-1001</td> <td>Korean</td> </tr> <tr class="row-odd"><td>gb2312</td> <td>chinese, csiso58gb231280, euc- cn, euccn, eucgb2312-cn, gb2312-1980, gb2312-80, iso- ir-58</td> <td>Simplified Chinese</td> </tr> <tr class="row-even"><td>gbk</td> <td>936, cp936, ms936</td> <td>Unified Chinese</td> </tr> <tr class="row-odd"><td>gb18030</td> <td>gb18030-2000</td> <td>Unified Chinese</td> </tr> <tr class="row-even"><td>hz</td> <td>hzgb, hz-gb, hz-gb-2312</td> <td>Simplified Chinese</td> </tr> <tr class="row-odd"><td>iso2022_jp</td> <td>csiso2022jp, iso2022jp, iso-2022-jp</td> <td>Japanese</td> </tr> <tr class="row-even"><td>iso2022_jp_1</td> <td>iso2022jp-1, iso-2022-jp-1</td> <td>Japanese</td> </tr> <tr class="row-odd"><td>iso2022_jp_2</td> <td>iso2022jp-2, iso-2022-jp-2</td> <td>Japanese, Korean, Simplified Chinese, Western Europe, Greek</td> </tr> <tr class="row-even"><td>iso2022_jp_2004</td> <td>iso2022jp-2004, iso-2022-jp-2004</td> <td>Japanese</td> </tr> <tr class="row-odd"><td>iso2022_jp_3</td> <td>iso2022jp-3, iso-2022-jp-3</td> <td>Japanese</td> </tr> <tr class="row-even"><td>iso2022_jp_ext</td> <td>iso2022jp-ext, iso-2022-jp-ext</td> <td>Japanese</td> </tr> <tr class="row-odd"><td>iso2022_kr</td> <td>csiso2022kr, iso2022kr, iso-2022-kr</td> <td>Korean</td> </tr> <tr class="row-even"><td>latin_1</td> <td>iso-8859-1, iso8859-1, 8859, cp819, latin, latin1, L1</td> <td>West Europe</td> </tr> <tr class="row-odd"><td>iso8859_2</td> <td>iso-8859-2, latin2, L2</td> <td>Central and Eastern Europe</td> </tr> <tr class="row-even"><td>iso8859_3</td> <td>iso-8859-3, latin3, L3</td> <td>Esperanto, Maltese</td> </tr> <tr class="row-odd"><td>iso8859_4</td> <td>iso-8859-4, latin4, L4</td> <td>Baltic languages</td> </tr> <tr class="row-even"><td>iso8859_5</td> <td>iso-8859-5, cyrillic</td> <td>Bulgarian, Byelorussian, Macedonian, Russian, Serbian</td> </tr> <tr class="row-odd"><td>iso8859_6</td> <td>iso-8859-6, arabic</td> <td>Arabic</td> </tr> <tr class="row-even"><td>iso8859_7</td> <td>iso-8859-7, greek, greek8</td> <td>Greek</td> </tr> <tr class="row-odd"><td>iso8859_8</td> <td>iso-8859-8, hebrew</td> <td>Hebrew</td> </tr> <tr class="row-even"><td>iso8859_9</td> <td>iso-8859-9, latin5, L5</td> <td>Turkish</td> </tr> <tr class="row-odd"><td>iso8859_10</td> <td>iso-8859-10, latin6, L6</td> <td>Nordic languages</td> </tr> <tr class="row-even"><td>iso8859_13</td> <td>iso-8859-13, latin7, L7</td> <td>Baltic languages</td> </tr> <tr class="row-odd"><td>iso8859_14</td> <td>iso-8859-14, latin8, L8</td> <td>Celtic languages</td> </tr> <tr class="row-even"><td>iso8859_15</td> <td>iso-8859-15, latin9, L9</td> <td>Western Europe</td> </tr> <tr class="row-odd"><td>iso8859_16</td> <td>iso-8859-16, latin10, L10</td> <td>South-Eastern Europe</td> </tr> <tr class="row-even"><td>johab</td> <td>cp1361, ms1361</td> <td>Korean</td> </tr> <tr class="row-odd"><td>koi8_r</td> <td> </td> <td>Russian</td> </tr> <tr class="row-even"><td>koi8_u</td> <td> </td> <td>Ukrainian</td> </tr> <tr class="row-odd"><td>mac_cyrillic</td> <td>maccyrillic</td> <td>Bulgarian, Byelorussian, Macedonian, Russian, Serbian</td> </tr> <tr class="row-even"><td>mac_greek</td> <td>macgreek</td> <td>Greek</td> </tr> <tr class="row-odd"><td>mac_iceland</td> <td>maciceland</td> <td>Icelandic</td> </tr> <tr class="row-even"><td>mac_latin2</td> <td>maclatin2, maccentraleurope</td> <td>Central and Eastern Europe</td> </tr> <tr class="row-odd"><td>mac_roman</td> <td>macroman</td> <td>Western Europe</td> </tr> <tr class="row-even"><td>mac_turkish</td> <td>macturkish</td> <td>Turkish</td> </tr> <tr class="row-odd"><td>ptcp154</td> <td>csptcp154, pt154, cp154, cyrillic-asian</td> <td>Kazakh</td> </tr> <tr class="row-even"><td>shift_jis</td> <td>csshiftjis, shiftjis, sjis, s_jis</td> <td>Japanese</td> </tr> <tr class="row-odd"><td>shift_jis_2004</td> <td>shiftjis2004, sjis_2004, sjis2004</td> <td>Japanese</td> </tr> <tr class="row-even"><td>shift_jisx0213</td> <td>shiftjisx0213, sjisx0213, s_jisx0213</td> <td>Japanese</td> </tr> <tr class="row-odd"><td>utf_32</td> <td>U32, utf32</td> <td>all languages</td> </tr> <tr class="row-even"><td>utf_32_be</td> <td>UTF-32BE</td> <td>all languages</td> </tr> <tr class="row-odd"><td>utf_32_le</td> <td>UTF-32LE</td> <td>all languages</td> </tr> <tr class="row-even"><td>utf_16</td> <td>U16, utf16</td> <td>all languages</td> </tr> <tr class="row-odd"><td>utf_16_be</td> <td>UTF-16BE</td> <td>all languages (BMP only)</td> </tr> <tr class="row-even"><td>utf_16_le</td> <td>UTF-16LE</td> <td>all languages (BMP only)</td> </tr> <tr class="row-odd"><td>utf_7</td> <td>U7, unicode-1-1-utf-7</td> <td>all languages</td> </tr> <tr class="row-even"><td>utf_8</td> <td>U8, UTF, utf8</td> <td>all languages</td> </tr> <tr class="row-odd"><td>utf_8_sig</td> <td> </td> <td>all languages</td> </tr> </tbody> </table> <p>A number of codecs are specific to Python, so their codec names have no meaning outside Python. Some of them don’t convert from Unicode strings to byte strings, but instead use the property of the Python codecs machinery that any bijective function with one argument can be considered as an encoding.</p> <p>For the codecs listed below, the result in the “encoding” direction is always a byte string. The result of the “decoding” direction is listed as operand type in the table.</p> <table border="1" class="docutils"> <colgroup> <col width="22%" /> <col width="30%" /> <col width="18%" /> <col width="30%" /> </colgroup> <thead valign="bottom"> <tr class="row-odd"><th class="head">Codec</th> <th class="head">Aliases</th> <th class="head">Operand type</th> <th class="head">Purpose</th> </tr> </thead> <tbody valign="top"> <tr class="row-even"><td>base64_codec</td> <td>base64, base-64</td> <td>byte string</td> <td>Convert operand to MIME base64 (the result always includes a trailing <tt class="docutils literal"><span class="pre">'\n'</span></tt>)</td> </tr> <tr class="row-odd"><td>bz2_codec</td> <td>bz2</td> <td>byte string</td> <td>Compress the operand using bz2</td> </tr> <tr class="row-even"><td>hex_codec</td> <td>hex</td> <td>byte string</td> <td>Convert operand to hexadecimal representation, with two digits per byte</td> </tr> <tr class="row-odd"><td>idna</td> <td> </td> <td>Unicode string</td> <td>Implements <span class="target" id="index-1"></span><a class="rfc reference external" href="http://tools.ietf.org/html/rfc3490.html"><strong>RFC 3490</strong></a>, see also <a class="reference internal" href="#module-encodings.idna" title="encodings.idna: Internationalized Domain Names implementation"><tt class="xref py py-mod docutils literal"><span class="pre">encodings.idna</span></tt></a></td> </tr> <tr class="row-even"><td>mbcs</td> <td>dbcs</td> <td>Unicode string</td> <td>Windows only: Encode operand according to the ANSI codepage (CP_ACP)</td> </tr> <tr class="row-odd"><td>palmos</td> <td> </td> <td>Unicode string</td> <td>Encoding of PalmOS 3.5</td> </tr> <tr class="row-even"><td>punycode</td> <td> </td> <td>Unicode string</td> <td>Implements <span class="target" id="index-2"></span><a class="rfc reference external" href="http://tools.ietf.org/html/rfc3492.html"><strong>RFC 3492</strong></a></td> </tr> <tr class="row-odd"><td>quopri_codec</td> <td>quopri, quoted-printable, quotedprintable</td> <td>byte string</td> <td>Convert operand to MIME quoted printable</td> </tr> <tr class="row-even"><td>raw_unicode_escape</td> <td> </td> <td>Unicode string</td> <td>Produce a string that is suitable as raw Unicode literal in Python source code</td> </tr> <tr class="row-odd"><td>rot_13</td> <td>rot13</td> <td>Unicode string</td> <td>Returns the Caesar-cypher encryption of the operand</td> </tr> <tr class="row-even"><td>string_escape</td> <td> </td> <td>byte string</td> <td>Produce a string that is suitable as string literal in Python source code</td> </tr> <tr class="row-odd"><td>undefined</td> <td> </td> <td>any</td> <td>Raise an exception for all conversions. Can be used as the system encoding if no automatic <a class="reference internal" href="../glossary.html#term-coercion"><em class="xref std std-term">coercion</em></a> between byte and Unicode strings is desired.</td> </tr> <tr class="row-even"><td>unicode_escape</td> <td> </td> <td>Unicode string</td> <td>Produce a string that is suitable as Unicode literal in Python source code</td> </tr> <tr class="row-odd"><td>unicode_internal</td> <td> </td> <td>Unicode string</td> <td>Return the internal representation of the operand</td> </tr> <tr class="row-even"><td>uu_codec</td> <td>uu</td> <td>byte string</td> <td>Convert the operand using uuencode</td> </tr> <tr class="row-odd"><td>zlib_codec</td> <td>zip, zlib</td> <td>byte string</td> <td>Compress the operand using gzip</td> </tr> </tbody> </table> <p class="versionadded"> <span class="versionmodified">New in version 2.3: </span>The <tt class="docutils literal"><span class="pre">idna</span></tt> and <tt class="docutils literal"><span class="pre">punycode</span></tt> encodings.</p> </div> <div class="section" id="module-encodings.idna"> <span id="encodings-idna-internationalized-domain-names-in-applications"></span><h2>7.8.4. <a class="reference internal" href="#module-encodings.idna" title="encodings.idna: Internationalized Domain Names implementation"><tt class="xref py py-mod docutils literal"><span class="pre">encodings.idna</span></tt></a> — Internationalized Domain Names in Applications<a class="headerlink" href="#module-encodings.idna" title="Permalink to this headline">¶</a></h2> <p class="versionadded"> <span class="versionmodified">New in version 2.3.</span></p> <p>This module implements <span class="target" id="index-3"></span><a class="rfc reference external" href="http://tools.ietf.org/html/rfc3490.html"><strong>RFC 3490</strong></a> (Internationalized Domain Names in Applications) and <span class="target" id="index-4"></span><a class="rfc reference external" href="http://tools.ietf.org/html/rfc3492.html"><strong>RFC 3492</strong></a> (Nameprep: A Stringprep Profile for Internationalized Domain Names (IDN)). It builds upon the <tt class="docutils literal"><span class="pre">punycode</span></tt> encoding and <a class="reference internal" href="stringprep.html#module-stringprep" title="stringprep: String preparation, as per RFC 3453 (deprecated)"><tt class="xref py py-mod docutils literal"><span class="pre">stringprep</span></tt></a>.</p> <p>These RFCs together define a protocol to support non-ASCII characters in domain names. A domain name containing non-ASCII characters (such as <tt class="docutils literal"><span class="pre">www.Alliancefrançaise.nu</span></tt>) is converted into an ASCII-compatible encoding (ACE, such as <tt class="docutils literal"><span class="pre">www.xn--alliancefranaise-npb.nu</span></tt>). The ACE form of the domain name is then used in all places where arbitrary characters are not allowed by the protocol, such as DNS queries, HTTP <em class="mailheader">Host</em> fields, and so on. This conversion is carried out in the application; if possible invisible to the user: The application should transparently convert Unicode domain labels to IDNA on the wire, and convert back ACE labels to Unicode before presenting them to the user.</p> <p>Python supports this conversion in several ways: the <tt class="docutils literal"><span class="pre">idna</span></tt> codec performs conversion between Unicode and ACE, separating an input string into labels based on the separator characters defined in <a class="reference external" href="http://tools.ietf.org/html/rfc3490#section-3.1">section 3.1</a> (1) of <span class="target" id="index-5"></span><a class="rfc reference external" href="http://tools.ietf.org/html/rfc3490.html"><strong>RFC 3490</strong></a> and converting each label to ACE as required, and conversely separating an input byte string into labels based on the <tt class="docutils literal"><span class="pre">.</span></tt> separator and converting any ACE labels found into unicode. Furthermore, the <a class="reference internal" href="socket.html#module-socket" title="socket: Low-level networking interface."><tt class="xref py py-mod docutils literal"><span class="pre">socket</span></tt></a> module transparently converts Unicode host names to ACE, so that applications need not be concerned about converting host names themselves when they pass them to the socket module. On top of that, modules that have host names as function parameters, such as <a class="reference internal" href="httplib.html#module-httplib" title="httplib: HTTP and HTTPS protocol client (requires sockets)."><tt class="xref py py-mod docutils literal"><span class="pre">httplib</span></tt></a> and <a class="reference internal" href="ftplib.html#module-ftplib" title="ftplib: FTP protocol client (requires sockets)."><tt class="xref py py-mod docutils literal"><span class="pre">ftplib</span></tt></a>, accept Unicode host names (<a class="reference internal" href="httplib.html#module-httplib" title="httplib: HTTP and HTTPS protocol client (requires sockets)."><tt class="xref py py-mod docutils literal"><span class="pre">httplib</span></tt></a> then also transparently sends an IDNA hostname in the <em class="mailheader">Host</em> field if it sends that field at all).</p> <p>When receiving host names from the wire (such as in reverse name lookup), no automatic conversion to Unicode is performed: Applications wishing to present such host names to the user should decode them to Unicode.</p> <p>The module <a class="reference internal" href="#module-encodings.idna" title="encodings.idna: Internationalized Domain Names implementation"><tt class="xref py py-mod docutils literal"><span class="pre">encodings.idna</span></tt></a> also implements the nameprep procedure, which performs certain normalizations on host names, to achieve case-insensitivity of international domain names, and to unify similar characters. The nameprep functions can be used directly if desired.</p> <dl class="function"> <dt id="encodings.idna.nameprep"> <tt class="descclassname">encodings.idna.</tt><tt class="descname">nameprep</tt><big>(</big><em>label</em><big>)</big><a class="headerlink" href="#encodings.idna.nameprep" title="Permalink to this definition">¶</a></dt> <dd><p>Return the nameprepped version of <em>label</em>. The implementation currently assumes query strings, so <tt class="docutils literal"><span class="pre">AllowUnassigned</span></tt> is true.</p> </dd></dl> <dl class="function"> <dt id="encodings.idna.ToASCII"> <tt class="descclassname">encodings.idna.</tt><tt class="descname">ToASCII</tt><big>(</big><em>label</em><big>)</big><a class="headerlink" href="#encodings.idna.ToASCII" title="Permalink to this definition">¶</a></dt> <dd><p>Convert a label to ASCII, as specified in <span class="target" id="index-6"></span><a class="rfc reference external" href="http://tools.ietf.org/html/rfc3490.html"><strong>RFC 3490</strong></a>. <tt class="docutils literal"><span class="pre">UseSTD3ASCIIRules</span></tt> is assumed to be false.</p> </dd></dl> <dl class="function"> <dt id="encodings.idna.ToUnicode"> <tt class="descclassname">encodings.idna.</tt><tt class="descname">ToUnicode</tt><big>(</big><em>label</em><big>)</big><a class="headerlink" href="#encodings.idna.ToUnicode" title="Permalink to this definition">¶</a></dt> <dd><p>Convert a label to Unicode, as specified in <span class="target" id="index-7"></span><a class="rfc reference external" href="http://tools.ietf.org/html/rfc3490.html"><strong>RFC 3490</strong></a>.</p> </dd></dl> </div> <div class="section" id="module-encodings.utf_8_sig"> <span id="encodings-utf-8-sig-utf-8-codec-with-bom-signature"></span><h2>7.8.5. <a class="reference internal" href="#module-encodings.utf_8_sig" title="encodings.utf_8_sig: UTF-8 codec with BOM signature"><tt class="xref py py-mod docutils literal"><span class="pre">encodings.utf_8_sig</span></tt></a> — UTF-8 codec with BOM signature<a class="headerlink" href="#module-encodings.utf_8_sig" title="Permalink to this headline">¶</a></h2> <p class="versionadded"> <span class="versionmodified">New in version 2.5.</span></p> <p>This module implements a variant of the UTF-8 codec: On encoding a UTF-8 encoded BOM will be prepended to the UTF-8 encoded bytes. For the stateful encoder this is only done once (on the first write to the byte stream). For decoding an optional UTF-8 encoded BOM at the start of the data will be skipped.</p> </div> </div> </div> </div> </div> <div class="sphinxsidebar"> <div class="sphinxsidebarwrapper"> <h3><a href="../contents.html">Table Of Contents</a></h3> <ul> <li><a class="reference internal" href="#">7.8. <tt class="docutils literal"><span class="pre">codecs</span></tt> — Codec registry and base classes</a><ul> <li><a class="reference internal" href="#codec-base-classes">7.8.1. Codec Base Classes</a><ul> <li><a class="reference internal" href="#codec-objects">7.8.1.1. Codec Objects</a></li> <li><a class="reference internal" href="#incrementalencoder-objects">7.8.1.2. IncrementalEncoder Objects</a></li> <li><a class="reference internal" href="#incrementaldecoder-objects">7.8.1.3. IncrementalDecoder Objects</a></li> <li><a class="reference internal" href="#streamwriter-objects">7.8.1.4. StreamWriter Objects</a></li> <li><a class="reference internal" href="#streamreader-objects">7.8.1.5. StreamReader Objects</a></li> <li><a class="reference internal" href="#streamreaderwriter-objects">7.8.1.6. StreamReaderWriter Objects</a></li> <li><a class="reference internal" href="#streamrecoder-objects">7.8.1.7. StreamRecoder Objects</a></li> </ul> </li> <li><a class="reference internal" href="#encodings-and-unicode">7.8.2. Encodings and Unicode</a></li> <li><a class="reference internal" href="#standard-encodings">7.8.3. Standard Encodings</a></li> <li><a class="reference internal" href="#module-encodings.idna">7.8.4. <tt class="docutils literal"><span class="pre">encodings.idna</span></tt> — Internationalized Domain Names in Applications</a></li> <li><a class="reference internal" href="#module-encodings.utf_8_sig">7.8.5. <tt class="docutils literal"><span class="pre">encodings.utf_8_sig</span></tt> — UTF-8 codec with BOM signature</a></li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="textwrap.html" title="previous chapter">7.7. <tt class="docutils literal"><span class="pre">textwrap</span></tt> — Text wrapping and filling</a></p> <h4>Next topic</h4> <p class="topless"><a href="unicodedata.html" title="next chapter">7.9. <tt class="docutils literal"><span class="pre">unicodedata</span></tt> — Unicode Database</a></p> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../bugs.html">Report a Bug</a></li> <li><a href="../_sources/library/codecs.txt" rel="nofollow">Show Source</a></li> </ul> <div id="searchbox" style="display: none"> <h3>Quick search</h3> <form class="search" action="../search.html" method="get"> <input 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> <p class="searchtip" style="font-size: 90%"> Enter search terms or a module, class or function name. </p> </div> <script type="text/javascript">$('#searchbox').show(0);</script> </div> </div> <div class="clearer"></div> </div> <div class="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="unicodedata.html" title="7.9. unicodedata — Unicode Database" >next</a> |</li> <li class="right" > <a href="textwrap.html" title="7.7. textwrap — Text wrapping and filling" >previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="http://www.python.org/">Python</a> »</li> <li> <a href="../index.html">Python 2.7.5 documentation</a> » </li> <li><a href="index.html" >The Python Standard Library</a> »</li> <li><a href="strings.html" >7. String Services</a> »</li> </ul> </div> <div class="footer"> © <a href="../copyright.html">Copyright</a> 1990-2019, Python Software Foundation. <br /> The Python Software Foundation is a non-profit corporation. <a href="http://www.python.org/psf/donations/">Please donate.</a> <br /> Last updated on Jul 03, 2019. <a href="../bugs.html">Found a bug</a>? <br /> Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3. </div> </body> </html>
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