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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="X-UA-Compatible" content="IE=Edge" /> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>18.2. json — JSON encoder and decoder — Python 2.7.18 documentation</title> <link rel="stylesheet" href="../_static/classic.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <script type="text/javascript" id="documentation_options" data-url_root="../" src="../_static/documentation_options.js"></script> <script type="text/javascript" src="../_static/jquery.js"></script> <script type="text/javascript" src="../_static/underscore.js"></script> <script type="text/javascript" src="../_static/doctools.js"></script> <script type="text/javascript" src="../_static/language_data.js"></script> <script type="text/javascript" src="../_static/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 2.7.18 documentation" href="../_static/opensearch.xml"/> <link rel="author" title="About these documents" href="../about.html" /> <link rel="index" title="Index" href="../genindex.html" /> <link rel="search" title="Search" href="../search.html" /> <link rel="copyright" title="Copyright" href="../copyright.html" /> <link rel="next" title="18.3. mailcap — Mailcap file handling" href="mailcap.html" /> <link rel="prev" title="18.1.11. email: Examples" href="email-examples.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="file:///usr/share/doc/python2.7/html/library/json.html" /> <script type="text/javascript" src="../_static/copybutton.js"></script> </head><body> <div id="outdated-warning" style="padding: .5em; text-align: center; background-color: #FFBABA; color: #6A0E0E;"> This document is for an old version of Python that is <a href="https://devguide.python.org/devcycle/#end-of-life-branches">no longer supported</a>. You should install the python3 and python3-doc packages and read the <a href="file:///usr/share/doc/python3-doc/html/library/json.html"> Python documentation for the Python3 version packaged in this release</a>. </div> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" accesskey="I">index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="mailcap.html" title="18.3. mailcap — Mailcap file handling" accesskey="N">next</a> |</li> <li class="right" > <a href="email-examples.html" title="18.1.11. email: Examples" accesskey="P">previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li> <a href="../index.html">Python 2.7.18 documentation</a> » </li> <li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> »</li> <li class="nav-item nav-item-2"><a href="netdata.html" accesskey="U">18. Internet Data Handling</a> »</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <div class="section" id="module-json"> <span id="json-json-encoder-and-decoder"></span><h1>18.2. <a class="reference internal" href="#module-json" title="json: Encode and decode the JSON format."><code class="xref py py-mod docutils literal notranslate"><span class="pre">json</span></code></a> — JSON encoder and decoder<a class="headerlink" href="#module-json" title="Permalink to this headline">¶</a></h1> <div class="versionadded"> <p><span class="versionmodified">New in version 2.6.</span></p> </div> <p><a class="reference external" href="http://json.org">JSON (JavaScript Object Notation)</a>, specified by <span class="target" id="index-0"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc7159.html"><strong>RFC 7159</strong></a> (which obsoletes <span class="target" id="index-1"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc4627.html"><strong>RFC 4627</strong></a>) and by <a class="reference external" href="http://www.ecma-international.org/publications/standards/Ecma-404.htm">ECMA-404</a>, is a lightweight data interchange format inspired by <a class="reference external" href="https://en.wikipedia.org/wiki/JavaScript">JavaScript</a> object literal syntax (although it is not a strict subset of JavaScript <a class="footnote-reference" href="#rfc-errata" id="id1">[1]</a> ).</p> <p><a class="reference internal" href="#module-json" title="json: Encode and decode the JSON format."><code class="xref py py-mod docutils literal notranslate"><span class="pre">json</span></code></a> exposes an API familiar to users of the standard library <a class="reference internal" href="marshal.html#module-marshal" title="marshal: Convert Python objects to streams of bytes and back (with different constraints)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">marshal</span></code></a> and <a class="reference internal" href="pickle.html#module-pickle" title="pickle: Convert Python objects to streams of bytes and back."><code class="xref py py-mod docutils literal notranslate"><span class="pre">pickle</span></code></a> modules.</p> <p>Encoding basic Python object hierarchies:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">json</span> <span class="gp">>>> </span><span class="n">json</span><span class="o">.</span><span class="n">dumps</span><span class="p">([</span><span class="s1">'foo'</span><span class="p">,</span> <span class="p">{</span><span class="s1">'bar'</span><span class="p">:</span> <span class="p">(</span><span class="s1">'baz'</span><span class="p">,</span> <span class="kc">None</span><span class="p">,</span> <span class="mf">1.0</span><span class="p">,</span> <span class="mi">2</span><span class="p">)}])</span> <span class="go">'["foo", {"bar": ["baz", null, 1.0, 2]}]'</span> <span class="gp">>>> </span><span class="nb">print</span> <span class="n">json</span><span class="o">.</span><span class="n">dumps</span><span class="p">(</span><span class="s2">"</span><span class="se">\"</span><span class="s2">foo</span><span class="se">\b</span><span class="s2">ar"</span><span class="p">)</span> <span class="go">"\"foo\bar"</span> <span class="gp">>>> </span><span class="nb">print</span> <span class="n">json</span><span class="o">.</span><span class="n">dumps</span><span class="p">(</span><span class="sa">u</span><span class="s1">'</span><span class="se">\u1234</span><span class="s1">'</span><span class="p">)</span> <span class="go">"\u1234"</span> <span class="gp">>>> </span><span class="nb">print</span> <span class="n">json</span><span class="o">.</span><span class="n">dumps</span><span class="p">(</span><span class="s1">'</span><span class="se">\\</span><span class="s1">'</span><span class="p">)</span> <span class="go">"\\"</span> <span class="gp">>>> </span><span class="nb">print</span> <span class="n">json</span><span class="o">.</span><span class="n">dumps</span><span class="p">({</span><span class="s2">"c"</span><span class="p">:</span> <span class="mi">0</span><span class="p">,</span> <span class="s2">"b"</span><span class="p">:</span> <span class="mi">0</span><span class="p">,</span> <span class="s2">"a"</span><span class="p">:</span> <span class="mi">0</span><span class="p">},</span> <span class="n">sort_keys</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span> <span class="go">{"a": 0, "b": 0, "c": 0}</span> <span class="gp">>>> </span><span class="kn">from</span> <span class="nn">StringIO</span> <span class="k">import</span> <span class="n">StringIO</span> <span class="gp">>>> </span><span class="n">io</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">()</span> <span class="gp">>>> </span><span class="n">json</span><span class="o">.</span><span class="n">dump</span><span class="p">([</span><span class="s1">'streaming API'</span><span class="p">],</span> <span class="n">io</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">io</span><span class="o">.</span><span class="n">getvalue</span><span class="p">()</span> <span class="go">'["streaming API"]'</span> </pre></div> </div> <p>Compact encoding:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">json</span> <span class="gp">>>> </span><span class="n">json</span><span class="o">.</span><span class="n">dumps</span><span class="p">([</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,{</span><span class="s1">'4'</span><span class="p">:</span> <span class="mi">5</span><span class="p">,</span> <span class="s1">'6'</span><span class="p">:</span> <span class="mi">7</span><span class="p">}],</span> <span class="n">separators</span><span class="o">=</span><span class="p">(</span><span class="s1">','</span><span class="p">,</span><span class="s1">':'</span><span class="p">))</span> <span class="go">'[1,2,3,{"4":5,"6":7}]'</span> </pre></div> </div> <p>Pretty printing:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">json</span> <span class="gp">>>> </span><span class="nb">print</span> <span class="n">json</span><span class="o">.</span><span class="n">dumps</span><span class="p">({</span><span class="s1">'4'</span><span class="p">:</span> <span class="mi">5</span><span class="p">,</span> <span class="s1">'6'</span><span class="p">:</span> <span class="mi">7</span><span class="p">},</span> <span class="n">sort_keys</span><span class="o">=</span><span class="kc">True</span><span class="p">,</span> <span class="gp">... </span> <span class="n">indent</span><span class="o">=</span><span class="mi">4</span><span class="p">,</span> <span class="n">separators</span><span class="o">=</span><span class="p">(</span><span class="s1">','</span><span class="p">,</span> <span class="s1">': '</span><span class="p">))</span> <span class="go">{</span> <span class="go"> "4": 5,</span> <span class="go"> "6": 7</span> <span class="go">}</span> </pre></div> </div> <p>Decoding JSON:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">json</span> <span class="gp">>>> </span><span class="n">json</span><span class="o">.</span><span class="n">loads</span><span class="p">(</span><span class="s1">'["foo", {"bar":["baz", null, 1.0, 2]}]'</span><span class="p">)</span> <span class="go">[u'foo', {u'bar': [u'baz', None, 1.0, 2]}]</span> <span class="gp">>>> </span><span class="n">json</span><span class="o">.</span><span class="n">loads</span><span class="p">(</span><span class="s1">'"</span><span class="se">\\</span><span class="s1">"foo</span><span class="se">\\</span><span class="s1">bar"'</span><span class="p">)</span> <span class="go">u'"foo\x08ar'</span> <span class="gp">>>> </span><span class="kn">from</span> <span class="nn">StringIO</span> <span class="k">import</span> <span class="n">StringIO</span> <span class="gp">>>> </span><span class="n">io</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s1">'["streaming API"]'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">json</span><span class="o">.</span><span class="n">load</span><span class="p">(</span><span class="n">io</span><span class="p">)</span> <span class="go">[u'streaming API']</span> </pre></div> </div> <p>Specializing JSON object decoding:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">json</span> <span class="gp">>>> </span><span class="k">def</span> <span class="nf">as_complex</span><span class="p">(</span><span class="n">dct</span><span class="p">):</span> <span class="gp">... </span> <span class="k">if</span> <span class="s1">'__complex__'</span> <span class="ow">in</span> <span class="n">dct</span><span class="p">:</span> <span class="gp">... </span> <span class="k">return</span> <span class="nb">complex</span><span class="p">(</span><span class="n">dct</span><span class="p">[</span><span class="s1">'real'</span><span class="p">],</span> <span class="n">dct</span><span class="p">[</span><span class="s1">'imag'</span><span class="p">])</span> <span class="gp">... </span> <span class="k">return</span> <span class="n">dct</span> <span class="gp">...</span> <span class="gp">>>> </span><span class="n">json</span><span class="o">.</span><span class="n">loads</span><span class="p">(</span><span class="s1">'{"__complex__": true, "real": 1, "imag": 2}'</span><span class="p">,</span> <span class="gp">... </span> <span class="n">object_hook</span><span class="o">=</span><span class="n">as_complex</span><span class="p">)</span> <span class="go">(1+2j)</span> <span class="gp">>>> </span><span class="kn">import</span> <span class="nn">decimal</span> <span class="gp">>>> </span><span class="n">json</span><span class="o">.</span><span class="n">loads</span><span class="p">(</span><span class="s1">'1.1'</span><span class="p">,</span> <span class="n">parse_float</span><span class="o">=</span><span class="n">decimal</span><span class="o">.</span><span class="n">Decimal</span><span class="p">)</span> <span class="go">Decimal('1.1')</span> </pre></div> </div> <p>Extending <a class="reference internal" href="#json.JSONEncoder" title="json.JSONEncoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">JSONEncoder</span></code></a>:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">json</span> <span class="gp">>>> </span><span class="k">class</span> <span class="nc">ComplexEncoder</span><span class="p">(</span><span class="n">json</span><span class="o">.</span><span class="n">JSONEncoder</span><span class="p">):</span> <span class="gp">... </span> <span class="k">def</span> <span class="nf">default</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">obj</span><span class="p">):</span> <span class="gp">... </span> <span class="k">if</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">obj</span><span class="p">,</span> <span class="nb">complex</span><span class="p">):</span> <span class="gp">... </span> <span class="k">return</span> <span class="p">[</span><span class="n">obj</span><span class="o">.</span><span class="n">real</span><span class="p">,</span> <span class="n">obj</span><span class="o">.</span><span class="n">imag</span><span class="p">]</span> <span class="gp">... </span> <span class="c1"># Let the base class default method raise the TypeError</span> <span class="gp">... </span> <span class="k">return</span> <span class="n">json</span><span class="o">.</span><span class="n">JSONEncoder</span><span class="o">.</span><span class="n">default</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">obj</span><span class="p">)</span> <span class="gp">...</span> <span class="gp">>>> </span><span class="n">json</span><span class="o">.</span><span class="n">dumps</span><span class="p">(</span><span class="mi">2</span> <span class="o">+</span> <span class="mi">1</span><span class="n">j</span><span class="p">,</span> <span class="bp">cls</span><span class="o">=</span><span class="n">ComplexEncoder</span><span class="p">)</span> <span class="go">'[2.0, 1.0]'</span> <span class="gp">>>> </span><span class="n">ComplexEncoder</span><span class="p">()</span><span class="o">.</span><span class="n">encode</span><span class="p">(</span><span class="mi">2</span> <span class="o">+</span> <span class="mi">1</span><span class="n">j</span><span class="p">)</span> <span class="go">'[2.0, 1.0]'</span> <span class="gp">>>> </span><span class="nb">list</span><span class="p">(</span><span class="n">ComplexEncoder</span><span class="p">()</span><span class="o">.</span><span class="n">iterencode</span><span class="p">(</span><span class="mi">2</span> <span class="o">+</span> <span class="mi">1</span><span class="n">j</span><span class="p">))</span> <span class="go">['[', '2.0', ', ', '1.0', ']']</span> </pre></div> </div> <p>Using <code class="xref py py-mod docutils literal notranslate"><span class="pre">json.tool</span></code> from the shell to validate and pretty-print:</p> <div class="highlight-none notranslate"><div class="highlight"><pre><span></span>$ echo '{"json":"obj"}' | python -m json.tool { "json": "obj" } $ echo '{1.2:3.4}' | python -mjson.tool Expecting property name enclosed in double quotes: line 1 column 2 (char 1) </pre></div> </div> <div class="admonition note"> <p class="first admonition-title">Note</p> <p class="last">JSON is a subset of <a class="reference external" href="http://yaml.org/">YAML</a> 1.2. The JSON produced by this module’s default settings (in particular, the default <em>separators</em> value) is also a subset of YAML 1.0 and 1.1. This module can thus also be used as a YAML serializer.</p> </div> <div class="section" id="basic-usage"> <h2>18.2.1. Basic Usage<a class="headerlink" href="#basic-usage" title="Permalink to this headline">¶</a></h2> <dl class="function"> <dt id="json.dump"> <code class="descclassname">json.</code><code class="descname">dump</code><span class="sig-paren">(</span><em>obj</em>, <em>fp</em>, <em>skipkeys=False</em>, <em>ensure_ascii=True</em>, <em>check_circular=True</em>, <em>allow_nan=True</em>, <em>cls=None</em>, <em>indent=None</em>, <em>separators=None</em>, <em>encoding="utf-8"</em>, <em>default=None</em>, <em>sort_keys=False</em>, <em>**kw</em><span class="sig-paren">)</span><a class="headerlink" href="#json.dump" title="Permalink to this definition">¶</a></dt> <dd><p>Serialize <em>obj</em> as a JSON formatted stream to <em>fp</em> (a <code class="docutils literal notranslate"><span class="pre">.write()</span></code>-supporting <a class="reference internal" href="../glossary.html#term-file-like-object"><span class="xref std std-term">file-like object</span></a>) using this <a class="reference internal" href="#py-to-json-table"><span class="std std-ref">conversion table</span></a>.</p> <p>If <em>skipkeys</em> is true (default: <code class="docutils literal notranslate"><span class="pre">False</span></code>), then dict keys that are not of a basic type (<a class="reference internal" href="functions.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a>, <a class="reference internal" href="functions.html#unicode" title="unicode"><code class="xref py py-class docutils literal notranslate"><span class="pre">unicode</span></code></a>, <a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate"><span class="pre">int</span></code></a>, <a class="reference internal" href="functions.html#long" title="long"><code class="xref py py-class docutils literal notranslate"><span class="pre">long</span></code></a>, <a class="reference internal" href="functions.html#float" title="float"><code class="xref py py-class docutils literal notranslate"><span class="pre">float</span></code></a>, <a class="reference internal" href="functions.html#bool" title="bool"><code class="xref py py-class docutils literal notranslate"><span class="pre">bool</span></code></a>, <code class="docutils literal notranslate"><span class="pre">None</span></code>) will be skipped instead of raising a <a class="reference internal" href="exceptions.html#exceptions.TypeError" title="exceptions.TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>.</p> <p>If <em>ensure_ascii</em> is true (the default), all non-ASCII characters in the output are escaped with <code class="docutils literal notranslate"><span class="pre">\uXXXX</span></code> sequences, and the result is a <a class="reference internal" href="functions.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> instance consisting of ASCII characters only. If <em>ensure_ascii</em> is false, some chunks written to <em>fp</em> may be <a class="reference internal" href="functions.html#unicode" title="unicode"><code class="xref py py-class docutils literal notranslate"><span class="pre">unicode</span></code></a> instances. This usually happens because the input contains unicode strings or the <em>encoding</em> parameter is used. Unless <code class="docutils literal notranslate"><span class="pre">fp.write()</span></code> explicitly understands <a class="reference internal" href="functions.html#unicode" title="unicode"><code class="xref py py-class docutils literal notranslate"><span class="pre">unicode</span></code></a> (as in <a class="reference internal" href="codecs.html#codecs.getwriter" title="codecs.getwriter"><code class="xref py py-func docutils literal notranslate"><span class="pre">codecs.getwriter()</span></code></a>) this is likely to cause an error.</p> <p>If <em>check_circular</em> is false (default: <code class="docutils literal notranslate"><span class="pre">True</span></code>), then the circular reference check for container types will be skipped and a circular reference will result in an <a class="reference internal" href="exceptions.html#exceptions.OverflowError" title="exceptions.OverflowError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">OverflowError</span></code></a> (or worse).</p> <p>If <em>allow_nan</em> is false (default: <code class="docutils literal notranslate"><span class="pre">True</span></code>), then it will be a <a class="reference internal" href="exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> to serialize out of range <a class="reference internal" href="functions.html#float" title="float"><code class="xref py py-class docutils literal notranslate"><span class="pre">float</span></code></a> values (<code class="docutils literal notranslate"><span class="pre">nan</span></code>, <code class="docutils literal notranslate"><span class="pre">inf</span></code>, <code class="docutils literal notranslate"><span class="pre">-inf</span></code>) in strict compliance of the JSON specification. If <em>allow_nan</em> is true, their JavaScript equivalents (<code class="docutils literal notranslate"><span class="pre">NaN</span></code>, <code class="docutils literal notranslate"><span class="pre">Infinity</span></code>, <code class="docutils literal notranslate"><span class="pre">-Infinity</span></code>) will be used.</p> <p>If <em>indent</em> is a non-negative integer, then JSON array elements and object members will be pretty-printed with that indent level. An indent level of 0, or negative, will only insert newlines. <code class="docutils literal notranslate"><span class="pre">None</span></code> (the default) selects the most compact representation.</p> <div class="admonition note"> <p class="first admonition-title">Note</p> <p class="last">Since the default item separator is <code class="docutils literal notranslate"><span class="pre">',</span> <span class="pre">'</span></code>, the output might include trailing whitespace when <em>indent</em> is specified. You can use <code class="docutils literal notranslate"><span class="pre">separators=(',',</span> <span class="pre">':</span> <span class="pre">')</span></code> to avoid this.</p> </div> <p>If specified, <em>separators</em> should be an <code class="docutils literal notranslate"><span class="pre">(item_separator,</span> <span class="pre">key_separator)</span></code> tuple. By default, <code class="docutils literal notranslate"><span class="pre">(',</span> <span class="pre">',</span> <span class="pre">':</span> <span class="pre">')</span></code> are used. To get the most compact JSON representation, you should specify <code class="docutils literal notranslate"><span class="pre">(',',</span> <span class="pre">':')</span></code> to eliminate whitespace.</p> <p><em>encoding</em> is the character encoding for str instances, default is UTF-8.</p> <p>If specified, <em>default</em> should be a function that gets called for objects that can’t otherwise be serialized. It should return a JSON encodable version of the object or raise a <a class="reference internal" href="exceptions.html#exceptions.TypeError" title="exceptions.TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>. If not specified, <a class="reference internal" href="exceptions.html#exceptions.TypeError" title="exceptions.TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a> is raised.</p> <p>If <em>sort_keys</em> is true (default: <code class="docutils literal notranslate"><span class="pre">False</span></code>), then the output of dictionaries will be sorted by key.</p> <p>To use a custom <a class="reference internal" href="#json.JSONEncoder" title="json.JSONEncoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">JSONEncoder</span></code></a> subclass (e.g. one that overrides the <code class="xref py py-meth docutils literal notranslate"><span class="pre">default()</span></code> method to serialize additional types), specify it with the <em>cls</em> kwarg; otherwise <a class="reference internal" href="#json.JSONEncoder" title="json.JSONEncoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">JSONEncoder</span></code></a> is used.</p> <div class="admonition note"> <p class="first admonition-title">Note</p> <p class="last">Unlike <a class="reference internal" href="pickle.html#module-pickle" title="pickle: Convert Python objects to streams of bytes and back."><code class="xref py py-mod docutils literal notranslate"><span class="pre">pickle</span></code></a> and <a class="reference internal" href="marshal.html#module-marshal" title="marshal: Convert Python objects to streams of bytes and back (with different constraints)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">marshal</span></code></a>, JSON is not a framed protocol so trying to serialize more objects with repeated calls to <a class="reference internal" href="#json.dump" title="json.dump"><code class="xref py py-func docutils literal notranslate"><span class="pre">dump()</span></code></a> and the same <em>fp</em> will result in an invalid JSON file.</p> </div> </dd></dl> <dl class="function"> <dt id="json.dumps"> <code class="descclassname">json.</code><code class="descname">dumps</code><span class="sig-paren">(</span><em>obj</em>, <em>skipkeys=False</em>, <em>ensure_ascii=True</em>, <em>check_circular=True</em>, <em>allow_nan=True</em>, <em>cls=None</em>, <em>indent=None</em>, <em>separators=None</em>, <em>encoding="utf-8"</em>, <em>default=None</em>, <em>sort_keys=False</em>, <em>**kw</em><span class="sig-paren">)</span><a class="headerlink" href="#json.dumps" title="Permalink to this definition">¶</a></dt> <dd><p>Serialize <em>obj</em> to a JSON formatted <a class="reference internal" href="functions.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> using this <a class="reference internal" href="#py-to-json-table"><span class="std std-ref">conversion table</span></a>. If <em>ensure_ascii</em> is false, the result may contain non-ASCII characters and the return value may be a <a class="reference internal" href="functions.html#unicode" title="unicode"><code class="xref py py-class docutils literal notranslate"><span class="pre">unicode</span></code></a> instance.</p> <p>The arguments have the same meaning as in <a class="reference internal" href="#json.dump" title="json.dump"><code class="xref py py-func docutils literal notranslate"><span class="pre">dump()</span></code></a>.</p> <div class="admonition note"> <p class="first admonition-title">Note</p> <p class="last">Keys in key/value pairs of JSON are always of the type <a class="reference internal" href="functions.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a>. When a dictionary is converted into JSON, all the keys of the dictionary are coerced to strings. As a result of this, if a dictionary is converted into JSON and then back into a dictionary, the dictionary may not equal the original one. That is, <code class="docutils literal notranslate"><span class="pre">loads(dumps(x))</span> <span class="pre">!=</span> <span class="pre">x</span></code> if x has non-string keys.</p> </div> </dd></dl> <dl class="function"> <dt id="json.load"> <code class="descclassname">json.</code><code class="descname">load</code><span class="sig-paren">(</span><em>fp</em><span class="optional">[</span>, <em>encoding</em><span class="optional">[</span>, <em>cls</em><span class="optional">[</span>, <em>object_hook</em><span class="optional">[</span>, <em>parse_float</em><span class="optional">[</span>, <em>parse_int</em><span class="optional">[</span>, <em>parse_constant</em><span class="optional">[</span>, <em>object_pairs_hook</em><span class="optional">[</span>, <em>**kw</em><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#json.load" title="Permalink to this definition">¶</a></dt> <dd><p>Deserialize <em>fp</em> (a <code class="docutils literal notranslate"><span class="pre">.read()</span></code>-supporting <a class="reference internal" href="../glossary.html#term-file-like-object"><span class="xref std std-term">file-like object</span></a> containing a JSON document) to a Python object using this <a class="reference internal" href="#json-to-py-table"><span class="std std-ref">conversion table</span></a>.</p> <p>If the contents of <em>fp</em> are encoded with an ASCII based encoding other than UTF-8 (e.g. latin-1), then an appropriate <em>encoding</em> name must be specified. Encodings that are not ASCII based (such as UCS-2) are not allowed, and should be wrapped with <code class="docutils literal notranslate"><span class="pre">codecs.getreader(encoding)(fp)</span></code>, or simply decoded to a <a class="reference internal" href="functions.html#unicode" title="unicode"><code class="xref py py-class docutils literal notranslate"><span class="pre">unicode</span></code></a> object and passed to <a class="reference internal" href="#json.loads" title="json.loads"><code class="xref py py-func docutils literal notranslate"><span class="pre">loads()</span></code></a>.</p> <p><em>object_hook</em> is an optional function that will be called with the result of any object literal decoded (a <a class="reference internal" href="stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate"><span class="pre">dict</span></code></a>). The return value of <em>object_hook</em> will be used instead of the <a class="reference internal" href="stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate"><span class="pre">dict</span></code></a>. This feature can be used to implement custom decoders (e.g. <a class="reference external" href="http://www.jsonrpc.org">JSON-RPC</a> class hinting).</p> <p><em>object_pairs_hook</em> is an optional function that will be called with the result of any object literal decoded with an ordered list of pairs. The return value of <em>object_pairs_hook</em> will be used instead of the <a class="reference internal" href="stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate"><span class="pre">dict</span></code></a>. This feature can be used to implement custom decoders that rely on the order that the key and value pairs are decoded (for example, <a class="reference internal" href="collections.html#collections.OrderedDict" title="collections.OrderedDict"><code class="xref py py-func docutils literal notranslate"><span class="pre">collections.OrderedDict()</span></code></a> will remember the order of insertion). If <em>object_hook</em> is also defined, the <em>object_pairs_hook</em> takes priority.</p> <div class="versionchanged"> <p><span class="versionmodified">Changed in version 2.7: </span>Added support for <em>object_pairs_hook</em>.</p> </div> <p><em>parse_float</em>, if specified, will be called with the string of every JSON float to be decoded. By default, this is equivalent to <code class="docutils literal notranslate"><span class="pre">float(num_str)</span></code>. This can be used to use another datatype or parser for JSON floats (e.g. <a class="reference internal" href="decimal.html#decimal.Decimal" title="decimal.Decimal"><code class="xref py py-class docutils literal notranslate"><span class="pre">decimal.Decimal</span></code></a>).</p> <p><em>parse_int</em>, if specified, will be called with the string of every JSON int to be decoded. By default, this is equivalent to <code class="docutils literal notranslate"><span class="pre">int(num_str)</span></code>. This can be used to use another datatype or parser for JSON integers (e.g. <a class="reference internal" href="functions.html#float" title="float"><code class="xref py py-class docutils literal notranslate"><span class="pre">float</span></code></a>).</p> <p><em>parse_constant</em>, if specified, will be called with one of the following strings: <code class="docutils literal notranslate"><span class="pre">'-Infinity'</span></code>, <code class="docutils literal notranslate"><span class="pre">'Infinity'</span></code>, <code class="docutils literal notranslate"><span class="pre">'NaN'</span></code>. This can be used to raise an exception if invalid JSON numbers are encountered.</p> <div class="versionchanged"> <p><span class="versionmodified">Changed in version 2.7: </span><em>parse_constant</em> doesn’t get called on ‘null’, ‘true’, ‘false’ anymore.</p> </div> <p>To use a custom <a class="reference internal" href="#json.JSONDecoder" title="json.JSONDecoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">JSONDecoder</span></code></a> subclass, specify it with the <code class="docutils literal notranslate"><span class="pre">cls</span></code> kwarg; otherwise <a class="reference internal" href="#json.JSONDecoder" title="json.JSONDecoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">JSONDecoder</span></code></a> is used. Additional keyword arguments will be passed to the constructor of the class.</p> </dd></dl> <dl class="function"> <dt id="json.loads"> <code class="descclassname">json.</code><code class="descname">loads</code><span class="sig-paren">(</span><em>s</em><span class="optional">[</span>, <em>encoding</em><span class="optional">[</span>, <em>cls</em><span class="optional">[</span>, <em>object_hook</em><span class="optional">[</span>, <em>parse_float</em><span class="optional">[</span>, <em>parse_int</em><span class="optional">[</span>, <em>parse_constant</em><span class="optional">[</span>, <em>object_pairs_hook</em><span class="optional">[</span>, <em>**kw</em><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#json.loads" title="Permalink to this definition">¶</a></dt> <dd><p>Deserialize <em>s</em> (a <a class="reference internal" href="functions.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> or <a class="reference internal" href="functions.html#unicode" title="unicode"><code class="xref py py-class docutils literal notranslate"><span class="pre">unicode</span></code></a> instance containing a JSON document) to a Python object using this <a class="reference internal" href="#json-to-py-table"><span class="std std-ref">conversion table</span></a>.</p> <p>If <em>s</em> is a <a class="reference internal" href="functions.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> instance and is encoded with an ASCII based encoding other than UTF-8 (e.g. latin-1), then an appropriate <em>encoding</em> name must be specified. Encodings that are not ASCII based (such as UCS-2) are not allowed and should be decoded to <a class="reference internal" href="functions.html#unicode" title="unicode"><code class="xref py py-class docutils literal notranslate"><span class="pre">unicode</span></code></a> first.</p> <p>The other arguments have the same meaning as in <a class="reference internal" href="#json.load" title="json.load"><code class="xref py py-func docutils literal notranslate"><span class="pre">load()</span></code></a>.</p> </dd></dl> </div> <div class="section" id="encoders-and-decoders"> <h2>18.2.2. Encoders and Decoders<a class="headerlink" href="#encoders-and-decoders" title="Permalink to this headline">¶</a></h2> <dl class="class"> <dt id="json.JSONDecoder"> <em class="property">class </em><code class="descclassname">json.</code><code class="descname">JSONDecoder</code><span class="sig-paren">(</span><span class="optional">[</span><em>encoding</em><span class="optional">[</span>, <em>object_hook</em><span class="optional">[</span>, <em>parse_float</em><span class="optional">[</span>, <em>parse_int</em><span class="optional">[</span>, <em>parse_constant</em><span class="optional">[</span>, <em>strict</em><span class="optional">[</span>, <em>object_pairs_hook</em><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#json.JSONDecoder" title="Permalink to this definition">¶</a></dt> <dd><p>Simple JSON decoder.</p> <p>Performs the following translations in decoding by default:</p> <table border="1" class="docutils" id="json-to-py-table"> <colgroup> <col width="44%" /> <col width="56%" /> </colgroup> <thead valign="bottom"> <tr class="row-odd"><th class="head">JSON</th> <th class="head">Python</th> </tr> </thead> <tbody valign="top"> <tr class="row-even"><td>object</td> <td>dict</td> </tr> <tr class="row-odd"><td>array</td> <td>list</td> </tr> <tr class="row-even"><td>string</td> <td>unicode</td> </tr> <tr class="row-odd"><td>number (int)</td> <td>int, long</td> </tr> <tr class="row-even"><td>number (real)</td> <td>float</td> </tr> <tr class="row-odd"><td>true</td> <td>True</td> </tr> <tr class="row-even"><td>false</td> <td>False</td> </tr> <tr class="row-odd"><td>null</td> <td>None</td> </tr> </tbody> </table> <p>It also understands <code class="docutils literal notranslate"><span class="pre">NaN</span></code>, <code class="docutils literal notranslate"><span class="pre">Infinity</span></code>, and <code class="docutils literal notranslate"><span class="pre">-Infinity</span></code> as their corresponding <code class="docutils literal notranslate"><span class="pre">float</span></code> values, which is outside the JSON spec.</p> <p><em>encoding</em> determines the encoding used to interpret any <a class="reference internal" href="functions.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> objects decoded by this instance (UTF-8 by default). It has no effect when decoding <a class="reference internal" href="functions.html#unicode" title="unicode"><code class="xref py py-class docutils literal notranslate"><span class="pre">unicode</span></code></a> objects.</p> <p>Note that currently only encodings that are a superset of ASCII work, strings of other encodings should be passed in as <a class="reference internal" href="functions.html#unicode" title="unicode"><code class="xref py py-class docutils literal notranslate"><span class="pre">unicode</span></code></a>.</p> <p><em>object_hook</em>, if specified, will be called with the result of every JSON object decoded and its return value will be used in place of the given <a class="reference internal" href="stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate"><span class="pre">dict</span></code></a>. This can be used to provide custom deserializations (e.g. to support JSON-RPC class hinting).</p> <p><em>object_pairs_hook</em>, if specified will be called with the result of every JSON object decoded with an ordered list of pairs. The return value of <em>object_pairs_hook</em> will be used instead of the <a class="reference internal" href="stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate"><span class="pre">dict</span></code></a>. This feature can be used to implement custom decoders that rely on the order that the key and value pairs are decoded (for example, <a class="reference internal" href="collections.html#collections.OrderedDict" title="collections.OrderedDict"><code class="xref py py-func docutils literal notranslate"><span class="pre">collections.OrderedDict()</span></code></a> will remember the order of insertion). If <em>object_hook</em> is also defined, the <em>object_pairs_hook</em> takes priority.</p> <div class="versionchanged"> <p><span class="versionmodified">Changed in version 2.7: </span>Added support for <em>object_pairs_hook</em>.</p> </div> <p><em>parse_float</em>, if specified, will be called with the string of every JSON float to be decoded. By default, this is equivalent to <code class="docutils literal notranslate"><span class="pre">float(num_str)</span></code>. This can be used to use another datatype or parser for JSON floats (e.g. <a class="reference internal" href="decimal.html#decimal.Decimal" title="decimal.Decimal"><code class="xref py py-class docutils literal notranslate"><span class="pre">decimal.Decimal</span></code></a>).</p> <p><em>parse_int</em>, if specified, will be called with the string of every JSON int to be decoded. By default, this is equivalent to <code class="docutils literal notranslate"><span class="pre">int(num_str)</span></code>. This can be used to use another datatype or parser for JSON integers (e.g. <a class="reference internal" href="functions.html#float" title="float"><code class="xref py py-class docutils literal notranslate"><span class="pre">float</span></code></a>).</p> <p><em>parse_constant</em>, if specified, will be called with one of the following strings: <code class="docutils literal notranslate"><span class="pre">'-Infinity'</span></code>, <code class="docutils literal notranslate"><span class="pre">'Infinity'</span></code>, <code class="docutils literal notranslate"><span class="pre">'NaN'</span></code>. This can be used to raise an exception if invalid JSON numbers are encountered.</p> <p>If <em>strict</em> is false (<code class="docutils literal notranslate"><span class="pre">True</span></code> is the default), then control characters will be allowed inside strings. Control characters in this context are those with character codes in the 0–31 range, including <code class="docutils literal notranslate"><span class="pre">'\t'</span></code> (tab), <code class="docutils literal notranslate"><span class="pre">'\n'</span></code>, <code class="docutils literal notranslate"><span class="pre">'\r'</span></code> and <code class="docutils literal notranslate"><span class="pre">'\0'</span></code>.</p> <p>If the data being deserialized is not a valid JSON document, a <a class="reference internal" href="exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> will be raised.</p> <dl class="method"> <dt id="json.JSONDecoder.decode"> <code class="descname">decode</code><span class="sig-paren">(</span><em>s</em><span class="sig-paren">)</span><a class="headerlink" href="#json.JSONDecoder.decode" title="Permalink to this definition">¶</a></dt> <dd><p>Return the Python representation of <em>s</em> (a <a class="reference internal" href="functions.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> or <a class="reference internal" href="functions.html#unicode" title="unicode"><code class="xref py py-class docutils literal notranslate"><span class="pre">unicode</span></code></a> instance containing a JSON document).</p> </dd></dl> <dl class="method"> <dt id="json.JSONDecoder.raw_decode"> <code class="descname">raw_decode</code><span class="sig-paren">(</span><em>s</em><span class="sig-paren">)</span><a class="headerlink" href="#json.JSONDecoder.raw_decode" title="Permalink to this definition">¶</a></dt> <dd><p>Decode a JSON document from <em>s</em> (a <a class="reference internal" href="functions.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> or <a class="reference internal" href="functions.html#unicode" title="unicode"><code class="xref py py-class docutils literal notranslate"><span class="pre">unicode</span></code></a> beginning with a JSON document) and return a 2-tuple of the Python representation and the index in <em>s</em> where the document ended.</p> <p>This can be used to decode a JSON document from a string that may have extraneous data at the end.</p> </dd></dl> </dd></dl> <dl class="class"> <dt id="json.JSONEncoder"> <em class="property">class </em><code class="descclassname">json.</code><code class="descname">JSONEncoder</code><span class="sig-paren">(</span><span class="optional">[</span><em>skipkeys</em><span class="optional">[</span>, <em>ensure_ascii</em><span class="optional">[</span>, <em>check_circular</em><span class="optional">[</span>, <em>allow_nan</em><span class="optional">[</span>, <em>sort_keys</em><span class="optional">[</span>, <em>indent</em><span class="optional">[</span>, <em>separators</em><span class="optional">[</span>, <em>encoding</em><span class="optional">[</span>, <em>default</em><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#json.JSONEncoder" title="Permalink to this definition">¶</a></dt> <dd><p>Extensible JSON encoder for Python data structures.</p> <p>Supports the following objects and types by default:</p> <table border="1" class="docutils" id="py-to-json-table"> <colgroup> <col width="56%" /> <col width="44%" /> </colgroup> <thead valign="bottom"> <tr class="row-odd"><th class="head">Python</th> <th class="head">JSON</th> </tr> </thead> <tbody valign="top"> <tr class="row-even"><td>dict</td> <td>object</td> </tr> <tr class="row-odd"><td>list, tuple</td> <td>array</td> </tr> <tr class="row-even"><td>str, unicode</td> <td>string</td> </tr> <tr class="row-odd"><td>int, long, float</td> <td>number</td> </tr> <tr class="row-even"><td>True</td> <td>true</td> </tr> <tr class="row-odd"><td>False</td> <td>false</td> </tr> <tr class="row-even"><td>None</td> <td>null</td> </tr> </tbody> </table> <p>To extend this to recognize other objects, subclass and implement a <a class="reference internal" href="#json.JSONEncoder.default" title="json.JSONEncoder.default"><code class="xref py py-meth docutils literal notranslate"><span class="pre">default()</span></code></a> method with another method that returns a serializable object for <code class="docutils literal notranslate"><span class="pre">o</span></code> if possible, otherwise it should call the superclass implementation (to raise <a class="reference internal" href="exceptions.html#exceptions.TypeError" title="exceptions.TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>).</p> <p>If <em>skipkeys</em> is false (the default), then it is a <a class="reference internal" href="exceptions.html#exceptions.TypeError" title="exceptions.TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a> to attempt encoding of keys that are not str, int, long, float or <code class="docutils literal notranslate"><span class="pre">None</span></code>. If <em>skipkeys</em> is true, such items are simply skipped.</p> <p>If <em>ensure_ascii</em> is true (the default), all non-ASCII characters in the output are escaped with <code class="docutils literal notranslate"><span class="pre">\uXXXX</span></code> sequences, and the results are <a class="reference internal" href="functions.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> instances consisting of ASCII characters only. If <em>ensure_ascii</em> is false, a result may be a <a class="reference internal" href="functions.html#unicode" title="unicode"><code class="xref py py-class docutils literal notranslate"><span class="pre">unicode</span></code></a> instance. This usually happens if the input contains unicode strings or the <em>encoding</em> parameter is used.</p> <p>If <em>check_circular</em> is true (the default), then lists, dicts, and custom encoded objects will be checked for circular references during encoding to prevent an infinite recursion (which would cause an <a class="reference internal" href="exceptions.html#exceptions.OverflowError" title="exceptions.OverflowError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">OverflowError</span></code></a>). Otherwise, no such check takes place.</p> <p>If <em>allow_nan</em> is true (the default), then <code class="docutils literal notranslate"><span class="pre">NaN</span></code>, <code class="docutils literal notranslate"><span class="pre">Infinity</span></code>, and <code class="docutils literal notranslate"><span class="pre">-Infinity</span></code> will be encoded as such. This behavior is not JSON specification compliant, but is consistent with most JavaScript based encoders and decoders. Otherwise, it will be a <a class="reference internal" href="exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> to encode such floats.</p> <p>If <em>sort_keys</em> is true (default: <code class="docutils literal notranslate"><span class="pre">False</span></code>), then the output of dictionaries will be sorted by key; this is useful for regression tests to ensure that JSON serializations can be compared on a day-to-day basis.</p> <p>If <em>indent</em> is a non-negative integer (it is <code class="docutils literal notranslate"><span class="pre">None</span></code> by default), then JSON array elements and object members will be pretty-printed with that indent level. An indent level of 0 will only insert newlines. <code class="docutils literal notranslate"><span class="pre">None</span></code> is the most compact representation.</p> <div class="admonition note"> <p class="first admonition-title">Note</p> <p class="last">Since the default item separator is <code class="docutils literal notranslate"><span class="pre">',</span> <span class="pre">'</span></code>, the output might include trailing whitespace when <em>indent</em> is specified. You can use <code class="docutils literal notranslate"><span class="pre">separators=(',',</span> <span class="pre">':</span> <span class="pre">')</span></code> to avoid this.</p> </div> <p>If specified, <em>separators</em> should be an <code class="docutils literal notranslate"><span class="pre">(item_separator,</span> <span class="pre">key_separator)</span></code> tuple. By default, <code class="docutils literal notranslate"><span class="pre">(',</span> <span class="pre">',</span> <span class="pre">':</span> <span class="pre">')</span></code> are used. To get the most compact JSON representation, you should specify <code class="docutils literal notranslate"><span class="pre">(',',</span> <span class="pre">':')</span></code> to eliminate whitespace.</p> <p>If specified, <em>default</em> should be a function that gets called for objects that can’t otherwise be serialized. It should return a JSON encodable version of the object or raise a <a class="reference internal" href="exceptions.html#exceptions.TypeError" title="exceptions.TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>. If not specified, <a class="reference internal" href="exceptions.html#exceptions.TypeError" title="exceptions.TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a> is raised.</p> <p>If <em>encoding</em> is not <code class="docutils literal notranslate"><span class="pre">None</span></code>, then all input strings will be transformed into unicode using that encoding prior to JSON-encoding. The default is UTF-8.</p> <dl class="method"> <dt id="json.JSONEncoder.default"> <code class="descname">default</code><span class="sig-paren">(</span><em>o</em><span class="sig-paren">)</span><a class="headerlink" href="#json.JSONEncoder.default" title="Permalink to this definition">¶</a></dt> <dd><p>Implement this method in a subclass such that it returns a serializable object for <em>o</em>, or calls the base implementation (to raise a <a class="reference internal" href="exceptions.html#exceptions.TypeError" title="exceptions.TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>).</p> <p>For example, to support arbitrary iterators, you could implement default like this:</p> <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">default</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">o</span><span class="p">):</span> <span class="k">try</span><span class="p">:</span> <span class="n">iterable</span> <span class="o">=</span> <span class="nb">iter</span><span class="p">(</span><span class="n">o</span><span class="p">)</span> <span class="k">except</span> <span class="ne">TypeError</span><span class="p">:</span> <span class="k">pass</span> <span class="k">else</span><span class="p">:</span> <span class="k">return</span> <span class="nb">list</span><span class="p">(</span><span class="n">iterable</span><span class="p">)</span> <span class="c1"># Let the base class default method raise the TypeError</span> <span class="k">return</span> <span class="n">JSONEncoder</span><span class="o">.</span><span class="n">default</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">o</span><span class="p">)</span> </pre></div> </div> </dd></dl> <dl class="method"> <dt id="json.JSONEncoder.encode"> <code class="descname">encode</code><span class="sig-paren">(</span><em>o</em><span class="sig-paren">)</span><a class="headerlink" href="#json.JSONEncoder.encode" title="Permalink to this definition">¶</a></dt> <dd><p>Return a JSON string representation of a Python data structure, <em>o</em>. For example:</p> <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">JSONEncoder</span><span class="p">()</span><span class="o">.</span><span class="n">encode</span><span class="p">({</span><span class="s2">"foo"</span><span class="p">:</span> <span class="p">[</span><span class="s2">"bar"</span><span class="p">,</span> <span class="s2">"baz"</span><span class="p">]})</span> <span class="go">'{"foo": ["bar", "baz"]}'</span> </pre></div> </div> </dd></dl> <dl class="method"> <dt id="json.JSONEncoder.iterencode"> <code class="descname">iterencode</code><span class="sig-paren">(</span><em>o</em><span class="sig-paren">)</span><a class="headerlink" href="#json.JSONEncoder.iterencode" title="Permalink to this definition">¶</a></dt> <dd><p>Encode the given object, <em>o</em>, and yield each string representation as available. For example:</p> <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="k">for</span> <span class="n">chunk</span> <span class="ow">in</span> <span class="n">JSONEncoder</span><span class="p">()</span><span class="o">.</span><span class="n">iterencode</span><span class="p">(</span><span class="n">bigobject</span><span class="p">):</span> <span class="n">mysocket</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">chunk</span><span class="p">)</span> </pre></div> </div> </dd></dl> </dd></dl> </div> <div class="section" id="standard-compliance-and-interoperability"> <h2>18.2.3. Standard Compliance and Interoperability<a class="headerlink" href="#standard-compliance-and-interoperability" title="Permalink to this headline">¶</a></h2> <p>The JSON format is specified by <span class="target" id="index-2"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc7159.html"><strong>RFC 7159</strong></a> and by <a class="reference external" href="http://www.ecma-international.org/publications/standards/Ecma-404.htm">ECMA-404</a>. This section details this module’s level of compliance with the RFC. For simplicity, <a class="reference internal" href="#json.JSONEncoder" title="json.JSONEncoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">JSONEncoder</span></code></a> and <a class="reference internal" href="#json.JSONDecoder" title="json.JSONDecoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">JSONDecoder</span></code></a> subclasses, and parameters other than those explicitly mentioned, are not considered.</p> <p>This module does not comply with the RFC in a strict fashion, implementing some extensions that are valid JavaScript but not valid JSON. In particular:</p> <ul class="simple"> <li>Infinite and NaN number values are accepted and output;</li> <li>Repeated names within an object are accepted, and only the value of the last name-value pair is used.</li> </ul> <p>Since the RFC permits RFC-compliant parsers to accept input texts that are not RFC-compliant, this module’s deserializer is technically RFC-compliant under default settings.</p> <div class="section" id="character-encodings"> <h3>18.2.3.1. Character Encodings<a class="headerlink" href="#character-encodings" title="Permalink to this headline">¶</a></h3> <p>The RFC requires that JSON be represented using either UTF-8, UTF-16, or UTF-32, with UTF-8 being the recommended default for maximum interoperability. Accordingly, this module uses UTF-8 as the default for its <em>encoding</em> parameter.</p> <p>This module’s deserializer only directly works with ASCII-compatible encodings; UTF-16, UTF-32, and other ASCII-incompatible encodings require the use of workarounds described in the documentation for the deserializer’s <em>encoding</em> parameter.</p> <p>As permitted, though not required, by the RFC, this module’s serializer sets <em>ensure_ascii=True</em> by default, thus escaping the output so that the resulting strings only contain ASCII characters.</p> <p>The RFC prohibits adding a byte order mark (BOM) to the start of a JSON text, and this module’s serializer does not add a BOM to its output. The RFC permits, but does not require, JSON deserializers to ignore an initial BOM in their input. This module’s deserializer raises a <a class="reference internal" href="exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> when an initial BOM is present.</p> <p>The RFC does not explicitly forbid JSON strings which contain byte sequences that don’t correspond to valid Unicode characters (e.g. unpaired UTF-16 surrogates), but it does note that they may cause interoperability problems. By default, this module accepts and outputs (when present in the original <a class="reference internal" href="functions.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a>) code points for such sequences.</p> </div> <div class="section" id="infinite-and-nan-number-values"> <h3>18.2.3.2. Infinite and NaN Number Values<a class="headerlink" href="#infinite-and-nan-number-values" title="Permalink to this headline">¶</a></h3> <p>The RFC does not permit the representation of infinite or NaN number values. Despite that, by default, this module accepts and outputs <code class="docutils literal notranslate"><span class="pre">Infinity</span></code>, <code class="docutils literal notranslate"><span class="pre">-Infinity</span></code>, and <code class="docutils literal notranslate"><span class="pre">NaN</span></code> as if they were valid JSON number literal values:</p> <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="c1"># Neither of these calls raises an exception, but the results are not valid JSON</span> <span class="gp">>>> </span><span class="n">json</span><span class="o">.</span><span class="n">dumps</span><span class="p">(</span><span class="nb">float</span><span class="p">(</span><span class="s1">'-inf'</span><span class="p">))</span> <span class="go">'-Infinity'</span> <span class="gp">>>> </span><span class="n">json</span><span class="o">.</span><span class="n">dumps</span><span class="p">(</span><span class="nb">float</span><span class="p">(</span><span class="s1">'nan'</span><span class="p">))</span> <span class="go">'NaN'</span> <span class="gp">>>> </span><span class="c1"># Same when deserializing</span> <span class="gp">>>> </span><span class="n">json</span><span class="o">.</span><span class="n">loads</span><span class="p">(</span><span class="s1">'-Infinity'</span><span class="p">)</span> <span class="go">-inf</span> <span class="gp">>>> </span><span class="n">json</span><span class="o">.</span><span class="n">loads</span><span class="p">(</span><span class="s1">'NaN'</span><span class="p">)</span> <span class="go">nan</span> </pre></div> </div> <p>In the serializer, the <em>allow_nan</em> parameter can be used to alter this behavior. In the deserializer, the <em>parse_constant</em> parameter can be used to alter this behavior.</p> </div> <div class="section" id="repeated-names-within-an-object"> <h3>18.2.3.3. Repeated Names Within an Object<a class="headerlink" href="#repeated-names-within-an-object" title="Permalink to this headline">¶</a></h3> <p>The RFC specifies that the names within a JSON object should be unique, but does not mandate how repeated names in JSON objects should be handled. By default, this module does not raise an exception; instead, it ignores all but the last name-value pair for a given name:</p> <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">weird_json</span> <span class="o">=</span> <span class="s1">'{"x": 1, "x": 2, "x": 3}'</span> <span class="gp">>>> </span><span class="n">json</span><span class="o">.</span><span class="n">loads</span><span class="p">(</span><span class="n">weird_json</span><span class="p">)</span> <span class="go">{u'x': 3}</span> </pre></div> </div> <p>The <em>object_pairs_hook</em> parameter can be used to alter this behavior.</p> </div> <div class="section" id="top-level-non-object-non-array-values"> <h3>18.2.3.4. Top-level Non-Object, Non-Array Values<a class="headerlink" href="#top-level-non-object-non-array-values" title="Permalink to this headline">¶</a></h3> <p>The old version of JSON specified by the obsolete <span class="target" id="index-3"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc4627.html"><strong>RFC 4627</strong></a> required that the top-level value of a JSON text must be either a JSON object or array (Python <a class="reference internal" href="stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate"><span class="pre">dict</span></code></a> or <code class="xref py py-class docutils literal notranslate"><span class="pre">list</span></code>), and could not be a JSON null, boolean, number, or string value. <span class="target" id="index-4"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc7159.html"><strong>RFC 7159</strong></a> removed that restriction, and this module does not and has never implemented that restriction in either its serializer or its deserializer.</p> <p>Regardless, for maximum interoperability, you may wish to voluntarily adhere to the restriction yourself.</p> </div> <div class="section" id="implementation-limitations"> <h3>18.2.3.5. Implementation Limitations<a class="headerlink" href="#implementation-limitations" title="Permalink to this headline">¶</a></h3> <p>Some JSON deserializer implementations may set limits on:</p> <ul class="simple"> <li>the size of accepted JSON texts</li> <li>the maximum level of nesting of JSON objects and arrays</li> <li>the range and precision of JSON numbers</li> <li>the content and maximum length of JSON strings</li> </ul> <p>This module does not impose any such limits beyond those of the relevant Python datatypes themselves or the Python interpreter itself.</p> <p>When serializing to JSON, beware any such limitations in applications that may consume your JSON. In particular, it is common for JSON numbers to be deserialized into IEEE 754 double precision numbers and thus subject to that representation’s range and precision limitations. This is especially relevant when serializing Python <a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate"><span class="pre">int</span></code></a> values of extremely large magnitude, or when serializing instances of “exotic” numerical types such as <a class="reference internal" href="decimal.html#decimal.Decimal" title="decimal.Decimal"><code class="xref py py-class docutils literal notranslate"><span class="pre">decimal.Decimal</span></code></a>.</p> <p class="rubric">Footnotes</p> <table class="docutils footnote" frame="void" id="rfc-errata" rules="none"> <colgroup><col class="label" /><col /></colgroup> <tbody valign="top"> <tr><td class="label"><a class="fn-backref" href="#id1">[1]</a></td><td>As noted in <a class="reference external" href="https://www.rfc-editor.org/errata_search.php?rfc=7159">the errata for RFC 7159</a>, JSON permits literal U+2028 (LINE SEPARATOR) and U+2029 (PARAGRAPH SEPARATOR) characters in strings, whereas JavaScript (as of ECMAScript Edition 5.1) does not.</td></tr> </tbody> </table> </div> </div> </div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="main navigation"> <div class="sphinxsidebarwrapper"> <h3><a href="../contents.html">Table of Contents</a></h3> <ul> <li><a class="reference internal" href="#">18.2. <code class="docutils literal notranslate"><span class="pre">json</span></code> — JSON encoder and decoder</a><ul> <li><a class="reference internal" href="#basic-usage">18.2.1. Basic Usage</a></li> <li><a class="reference internal" href="#encoders-and-decoders">18.2.2. Encoders and Decoders</a></li> <li><a class="reference internal" href="#standard-compliance-and-interoperability">18.2.3. Standard Compliance and Interoperability</a><ul> <li><a class="reference internal" href="#character-encodings">18.2.3.1. Character Encodings</a></li> <li><a class="reference internal" href="#infinite-and-nan-number-values">18.2.3.2. Infinite and NaN Number Values</a></li> <li><a class="reference internal" href="#repeated-names-within-an-object">18.2.3.3. Repeated Names Within an Object</a></li> <li><a class="reference internal" href="#top-level-non-object-non-array-values">18.2.3.4. Top-level Non-Object, Non-Array Values</a></li> <li><a class="reference internal" href="#implementation-limitations">18.2.3.5. Implementation Limitations</a></li> </ul> </li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="email-examples.html" title="previous chapter">18.1.11. <code class="docutils literal notranslate"><span class="pre">email</span></code>: Examples</a></p> <h4>Next topic</h4> <p class="topless"><a href="mailcap.html" title="next chapter">18.3. <code class="docutils literal notranslate"><span class="pre">mailcap</span></code> — Mailcap file handling</a></p> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../_sources/library/json.rst.txt" rel="nofollow">Show Source</a></li> </ul> </div> <div id="searchbox" style="display: none" role="search"> <h3>Quick search</h3> <div class="searchformwrapper"> <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> </div> </div> <script type="text/javascript">$('#searchbox').show(0);</script> </div> </div> <div class="clearer"></div> </div> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" >index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="mailcap.html" title="18.3. mailcap — Mailcap file handling" >next</a> |</li> <li class="right" > <a href="email-examples.html" title="18.1.11. email: Examples" >previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li> <a href="../index.html">Python 2.7.18 documentation</a> » </li> <li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> »</li> <li class="nav-item nav-item-2"><a href="netdata.html" >18. 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