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<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."><tt class="xref py py-mod docutils literal"><span class="pre">json</span></tt></a> — JSON encoder and decoder<a class="headerlink" href="#module-json" title="Permalink to this headline">¶</a></h1>
<p class="versionadded">
<span class="versionmodified">New in version 2.6.</span></p>
<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="http://tools.ietf.org/html/rfc4627.html"><strong>RFC 4627</strong></a>, is a lightweight data interchange format based on a subset of
<a class="reference external" href="http://en.wikipedia.org/wiki/JavaScript">JavaScript</a> syntax (<a class="reference external" href="http://www.ecma-international.org/publications/files/ECMA-ST-ARCH/ECMA-262,%203rd%20edition,%20December%201999.pdf">ECMA-262 3rd
edition</a>).</p>
<p><a class="reference internal" href="#module-json" title="json: Encode and decode the JSON format."><tt class="xref py py-mod docutils literal"><span class="pre">json</span></tt></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)."><tt class="xref py py-mod docutils literal"><span class="pre">marshal</span></tt></a> and <a class="reference internal" href="pickle.html#module-pickle" title="pickle: Convert Python objects to streams of bytes and back."><tt class="xref py py-mod docutils literal"><span class="pre">pickle</span></tt></a> modules.</p>
<p>Encoding basic Python object hierarchies:</p>
<div class="highlight-python"><div class="highlight"><pre><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="s">'foo'</span><span class="p">,</span> <span class="p">{</span><span class="s">'bar'</span><span class="p">:</span> <span class="p">(</span><span class="s">'baz'</span><span class="p">,</span> <span class="bp">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="k">print</span> <span class="n">json</span><span class="o">.</span><span class="n">dumps</span><span class="p">(</span><span class="s">"</span><span class="se">\"</span><span class="s">foo</span><span class="se">\b</span><span class="s">ar"</span><span class="p">)</span>
<span class="go">"\"foo\bar"</span>
<span class="gp">>>> </span><span class="k">print</span> <span class="n">json</span><span class="o">.</span><span class="n">dumps</span><span class="p">(</span><span class="s">u'</span><span class="se">\u1234</span><span class="s">'</span><span class="p">)</span>
<span class="go">"\u1234"</span>
<span class="gp">>>> </span><span class="k">print</span> <span class="n">json</span><span class="o">.</span><span class="n">dumps</span><span class="p">(</span><span class="s">'</span><span class="se">\\</span><span class="s">'</span><span class="p">)</span>
<span class="go">"\\"</span>
<span class="gp">>>> </span><span class="k">print</span> <span class="n">json</span><span class="o">.</span><span class="n">dumps</span><span class="p">({</span><span class="s">"c"</span><span class="p">:</span> <span class="mi">0</span><span class="p">,</span> <span class="s">"b"</span><span class="p">:</span> <span class="mi">0</span><span class="p">,</span> <span class="s">"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="bp">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="kn">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="s">'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-python"><div class="highlight"><pre><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="s">'4'</span><span class="p">:</span> <span class="mi">5</span><span class="p">,</span> <span class="s">'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="s">','</span><span class="p">,</span><span class="s">':'</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-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">json</span>
<span class="gp">>>> </span><span class="k">print</span> <span class="n">json</span><span class="o">.</span><span class="n">dumps</span><span class="p">({</span><span class="s">'4'</span><span class="p">:</span> <span class="mi">5</span><span class="p">,</span> <span class="s">'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="bp">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="s">','</span><span class="p">,</span> <span class="s">': '</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-python"><div class="highlight"><pre><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="s">'["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="s">'"</span><span class="se">\\</span><span class="s">"foo</span><span class="se">\\</span><span class="s">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="kn">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="s">'["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-python"><div class="highlight"><pre><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="s">'__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="s">'real'</span><span class="p">],</span> <span class="n">dct</span><span class="p">[</span><span class="s">'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="s">'{"__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="s">'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"><tt class="xref py py-class docutils literal"><span class="pre">JSONEncoder</span></tt></a>:</p>
<div class="highlight-python"><div class="highlight"><pre><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="c"># 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">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="n">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 json.tool from the shell to validate and pretty-print:</p>
<div class="highlight-none"><div class="highlight"><pre>$ echo '{"json":"obj"}' | python -mjson.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">
<tt class="descclassname">json.</tt><tt class="descname">dump</tt><big>(</big><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><big>)</big><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 <tt class="docutils literal"><span class="pre">.write()</span></tt>-supporting
<a class="reference internal" href="../glossary.html#term-file-like-object"><em class="xref std std-term">file-like object</em></a>) using this <a class="reference internal" href="#py-to-json-table"><em>conversion table</em></a>.</p>
<p>If <em>skipkeys</em> is <tt class="docutils literal"><span class="pre">True</span></tt> (default: <tt class="docutils literal"><span class="pre">False</span></tt>), then dict keys that are not
of a basic type (<a class="reference internal" href="functions.html#str" title="str"><tt class="xref py py-class docutils literal"><span class="pre">str</span></tt></a>, <a class="reference internal" href="functions.html#unicode" title="unicode"><tt class="xref py py-class docutils literal"><span class="pre">unicode</span></tt></a>, <a class="reference internal" href="functions.html#int" title="int"><tt class="xref py py-class docutils literal"><span class="pre">int</span></tt></a>, <a class="reference internal" href="functions.html#long" title="long"><tt class="xref py py-class docutils literal"><span class="pre">long</span></tt></a>,
<a class="reference internal" href="functions.html#float" title="float"><tt class="xref py py-class docutils literal"><span class="pre">float</span></tt></a>, <a class="reference internal" href="functions.html#bool" title="bool"><tt class="xref py py-class docutils literal"><span class="pre">bool</span></tt></a>, <tt class="docutils literal"><span class="pre">None</span></tt>) will be skipped instead of raising a
<a class="reference internal" href="exceptions.html#exceptions.TypeError" title="exceptions.TypeError"><tt class="xref py py-exc docutils literal"><span class="pre">TypeError</span></tt></a>.</p>
<p>If <em>ensure_ascii</em> is <tt class="docutils literal"><span class="pre">True</span></tt> (the default), all non-ASCII characters in the
output are escaped with <tt class="docutils literal"><span class="pre">\uXXXX</span></tt> sequences, and the result is a
<a class="reference internal" href="functions.html#str" title="str"><tt class="xref py py-class docutils literal"><span class="pre">str</span></tt></a> instance consisting of ASCII characters only. If
<em>ensure_ascii</em> is <tt class="docutils literal"><span class="pre">False</span></tt>, some chunks written to <em>fp</em> may be
<a class="reference internal" href="functions.html#unicode" title="unicode"><tt class="xref py py-class docutils literal"><span class="pre">unicode</span></tt></a> instances. This usually happens because the input contains
unicode strings or the <em>encoding</em> parameter is used. Unless <tt class="docutils literal"><span class="pre">fp.write()</span></tt>
explicitly understands <a class="reference internal" href="functions.html#unicode" title="unicode"><tt class="xref py py-class docutils literal"><span class="pre">unicode</span></tt></a> (as in <a class="reference internal" href="codecs.html#codecs.getwriter" title="codecs.getwriter"><tt class="xref py py-func docutils literal"><span class="pre">codecs.getwriter()</span></tt></a>)
this is likely to cause an error.</p>
<p>If <em>check_circular</em> is <tt class="docutils literal"><span class="pre">False</span></tt> (default: <tt class="docutils literal"><span class="pre">True</span></tt>), 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"><tt class="xref py py-exc docutils literal"><span class="pre">OverflowError</span></tt></a> (or worse).</p>
<p>If <em>allow_nan</em> is <tt class="docutils literal"><span class="pre">False</span></tt> (default: <tt class="docutils literal"><span class="pre">True</span></tt>), then it will be 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 serialize out of range <a class="reference internal" href="functions.html#float" title="float"><tt class="xref py py-class docutils literal"><span class="pre">float</span></tt></a> values (<tt class="docutils literal"><span class="pre">nan</span></tt>,
<tt class="docutils literal"><span class="pre">inf</span></tt>, <tt class="docutils literal"><span class="pre">-inf</span></tt>) in strict compliance of the JSON specification, instead of
using the JavaScript equivalents (<tt class="docutils literal"><span class="pre">NaN</span></tt>, <tt class="docutils literal"><span class="pre">Infinity</span></tt>, <tt class="docutils literal"><span class="pre">-Infinity</span></tt>).</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. <tt class="docutils literal"><span class="pre">None</span></tt> (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 <tt class="docutils literal"><span class="pre">',</span> <span class="pre">'</span></tt>, the output might include
trailing whitespace when <em>indent</em> is specified. You can use
<tt class="docutils literal"><span class="pre">separators=(',',</span> <span class="pre">':</span> <span class="pre">')</span></tt> to avoid this.</p>
</div>
<p>If <em>separators</em> is an <tt class="docutils literal"><span class="pre">(item_separator,</span> <span class="pre">dict_separator)</span></tt> tuple, then it
will be used instead of the default <tt class="docutils literal"><span class="pre">(',</span> <span class="pre">',</span> <span class="pre">':</span> <span class="pre">')</span></tt> separators. <tt class="docutils literal"><span class="pre">(',',</span>
<span class="pre">':')</span></tt> is the most compact JSON representation.</p>
<p><em>encoding</em> is the character encoding for str instances, default is UTF-8.</p>
<p><em>default(obj)</em> is a function that should return a serializable version of
<em>obj</em> or raise <a class="reference internal" href="exceptions.html#exceptions.TypeError" title="exceptions.TypeError"><tt class="xref py py-exc docutils literal"><span class="pre">TypeError</span></tt></a>. The default simply raises <a class="reference internal" href="exceptions.html#exceptions.TypeError" title="exceptions.TypeError"><tt class="xref py py-exc docutils literal"><span class="pre">TypeError</span></tt></a>.</p>
<p>If <em>sort_keys</em> is <tt class="docutils literal"><span class="pre">True</span></tt> (default: <tt class="docutils literal"><span class="pre">False</span></tt>), 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"><tt class="xref py py-class docutils literal"><span class="pre">JSONEncoder</span></tt></a> subclass (e.g. one that overrides the
<tt class="xref py py-meth docutils literal"><span class="pre">default()</span></tt> method to serialize additional types), specify it with the
<em>cls</em> kwarg; otherwise <a class="reference internal" href="#json.JSONEncoder" title="json.JSONEncoder"><tt class="xref py py-class docutils literal"><span class="pre">JSONEncoder</span></tt></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."><tt class="xref py py-mod docutils literal"><span class="pre">pickle</span></tt></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)."><tt class="xref py py-mod docutils literal"><span class="pre">marshal</span></tt></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"><tt class="xref py py-func docutils literal"><span class="pre">dump()</span></tt></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">
<tt class="descclassname">json.</tt><tt class="descname">dumps</tt><big>(</big><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><big>)</big><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"><tt class="xref py py-class docutils literal"><span class="pre">str</span></tt></a> using this <a class="reference internal" href="#py-to-json-table"><em>conversion
table</em></a>. If <em>ensure_ascii</em> is <tt class="docutils literal"><span class="pre">False</span></tt>, the result may
contain non-ASCII characters and the return value may be a <a class="reference internal" href="functions.html#unicode" title="unicode"><tt class="xref py py-class docutils literal"><span class="pre">unicode</span></tt></a>
instance.</p>
<p>The arguments have the same meaning as in <a class="reference internal" href="#json.dump" title="json.dump"><tt class="xref py py-func docutils literal"><span class="pre">dump()</span></tt></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"><tt class="xref py py-class docutils literal"><span class="pre">str</span></tt></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, <tt class="docutils literal"><span class="pre">loads(dumps(x))</span> <span class="pre">!=</span> <span class="pre">x</span></tt> if x has non-string
keys.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="json.load">
<tt class="descclassname">json.</tt><tt class="descname">load</tt><big>(</big><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><big>)</big><a class="headerlink" href="#json.load" title="Permalink to this definition">¶</a></dt>
<dd><p>Deserialize <em>fp</em> (a <tt class="docutils literal"><span class="pre">.read()</span></tt>-supporting <a class="reference internal" href="../glossary.html#term-file-like-object"><em class="xref std std-term">file-like object</em></a>
containing a JSON document) to a Python object using this <a class="reference internal" href="#json-to-py-table"><em>conversion
table</em></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 <tt class="docutils literal"><span class="pre">codecs.getreader(encoding)(fp)</span></tt>, or simply decoded
to a <a class="reference internal" href="functions.html#unicode" title="unicode"><tt class="xref py py-class docutils literal"><span class="pre">unicode</span></tt></a> object and passed to <a class="reference internal" href="#json.loads" title="json.loads"><tt class="xref py py-func docutils literal"><span class="pre">loads()</span></tt></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"><tt class="xref py py-class docutils literal"><span class="pre">dict</span></tt></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"><tt class="xref py py-class docutils literal"><span class="pre">dict</span></tt></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"><tt class="xref py py-class docutils literal"><span class="pre">dict</span></tt></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"><tt class="xref py py-func docutils literal"><span class="pre">collections.OrderedDict()</span></tt></a> will remember the order of insertion). If
<em>object_hook</em> is also defined, the <em>object_pairs_hook</em> takes priority.</p>
<p class="versionchanged">
<span class="versionmodified">Changed in version 2.7: </span>Added support for <em>object_pairs_hook</em>.</p>
<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 <tt class="docutils literal"><span class="pre">float(num_str)</span></tt>.
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"><tt class="xref py py-class docutils literal"><span class="pre">decimal.Decimal</span></tt></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 <tt class="docutils literal"><span class="pre">int(num_str)</span></tt>. 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"><tt class="xref py py-class docutils literal"><span class="pre">float</span></tt></a>).</p>
<p><em>parse_constant</em>, if specified, will be called with one of the following
strings: <tt class="docutils literal"><span class="pre">'-Infinity'</span></tt>, <tt class="docutils literal"><span class="pre">'Infinity'</span></tt>, <tt class="docutils literal"><span class="pre">'NaN'</span></tt>.
This can be used to raise an exception if invalid JSON numbers
are encountered.</p>
<p class="versionchanged">
<span class="versionmodified">Changed in version 2.7: </span><em>parse_constant</em> doesn’t get called on ‘null’, ‘true’, ‘false’ anymore.</p>
<p>To use a custom <a class="reference internal" href="#json.JSONDecoder" title="json.JSONDecoder"><tt class="xref py py-class docutils literal"><span class="pre">JSONDecoder</span></tt></a> subclass, specify it with the <tt class="docutils literal"><span class="pre">cls</span></tt>
kwarg; otherwise <a class="reference internal" href="#json.JSONDecoder" title="json.JSONDecoder"><tt class="xref py py-class docutils literal"><span class="pre">JSONDecoder</span></tt></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">
<tt class="descclassname">json.</tt><tt class="descname">loads</tt><big>(</big><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><big>)</big><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"><tt class="xref py py-class docutils literal"><span class="pre">str</span></tt></a> or <a class="reference internal" href="functions.html#unicode" title="unicode"><tt class="xref py py-class docutils literal"><span class="pre">unicode</span></tt></a> instance containing a JSON
document) to a Python object using this <a class="reference internal" href="#json-to-py-table"><em>conversion table</em></a>.</p>
<p>If <em>s</em> is a <a class="reference internal" href="functions.html#str" title="str"><tt class="xref py py-class docutils literal"><span class="pre">str</span></tt></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"><tt class="xref py py-class docutils literal"><span class="pre">unicode</span></tt></a> first.</p>
<p>The other arguments have the same meaning as in <a class="reference internal" href="#json.load" title="json.load"><tt class="xref py py-func docutils literal"><span class="pre">load()</span></tt></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><tt class="descclassname">json.</tt><tt class="descname">JSONDecoder</tt><big>(</big><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><big>)</big><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 <tt class="docutils literal"><span class="pre">NaN</span></tt>, <tt class="docutils literal"><span class="pre">Infinity</span></tt>, and <tt class="docutils literal"><span class="pre">-Infinity</span></tt> as their
corresponding <tt class="docutils literal"><span class="pre">float</span></tt> 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"><tt class="xref py py-class docutils literal"><span class="pre">str</span></tt></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"><tt class="xref py py-class docutils literal"><span class="pre">unicode</span></tt></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"><tt class="xref py py-class docutils literal"><span class="pre">unicode</span></tt></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"><tt class="xref py py-class docutils literal"><span class="pre">dict</span></tt></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"><tt class="xref py py-class docutils literal"><span class="pre">dict</span></tt></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"><tt class="xref py py-func docutils literal"><span class="pre">collections.OrderedDict()</span></tt></a> will remember the order of insertion). If
<em>object_hook</em> is also defined, the <em>object_pairs_hook</em> takes priority.</p>
<p class="versionchanged">
<span class="versionmodified">Changed in version 2.7: </span>Added support for <em>object_pairs_hook</em>.</p>
<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 <tt class="docutils literal"><span class="pre">float(num_str)</span></tt>.
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"><tt class="xref py py-class docutils literal"><span class="pre">decimal.Decimal</span></tt></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 <tt class="docutils literal"><span class="pre">int(num_str)</span></tt>. 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"><tt class="xref py py-class docutils literal"><span class="pre">float</span></tt></a>).</p>
<p><em>parse_constant</em>, if specified, will be called with one of the following
strings: <tt class="docutils literal"><span class="pre">'-Infinity'</span></tt>, <tt class="docutils literal"><span class="pre">'Infinity'</span></tt>, <tt class="docutils literal"><span class="pre">'NaN'</span></tt>, <tt class="docutils literal"><span class="pre">'null'</span></tt>, <tt class="docutils literal"><span class="pre">'true'</span></tt>,
<tt class="docutils literal"><span class="pre">'false'</span></tt>. This can be used to raise an exception if invalid JSON numbers
are encountered.</p>
<p>If <em>strict</em> is <tt class="docutils literal"><span class="pre">False</span></tt> (<tt class="docutils literal"><span class="pre">True</span></tt> 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 <tt class="docutils literal"><span class="pre">'\t'</span></tt> (tab),
<tt class="docutils literal"><span class="pre">'\n'</span></tt>, <tt class="docutils literal"><span class="pre">'\r'</span></tt> and <tt class="docutils literal"><span class="pre">'\0'</span></tt>.</p>
<dl class="method">
<dt id="json.JSONDecoder.decode">
<tt class="descname">decode</tt><big>(</big><em>s</em><big>)</big><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"><tt class="xref py py-class docutils literal"><span class="pre">str</span></tt></a> or
<a class="reference internal" href="functions.html#unicode" title="unicode"><tt class="xref py py-class docutils literal"><span class="pre">unicode</span></tt></a> instance containing a JSON document)</p>
</dd></dl>
<dl class="method">
<dt id="json.JSONDecoder.raw_decode">
<tt class="descname">raw_decode</tt><big>(</big><em>s</em><big>)</big><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"><tt class="xref py py-class docutils literal"><span class="pre">str</span></tt></a> or <a class="reference internal" href="functions.html#unicode" title="unicode"><tt class="xref py py-class docutils literal"><span class="pre">unicode</span></tt></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><tt class="descclassname">json.</tt><tt class="descname">JSONEncoder</tt><big>(</big><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><big>)</big><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"><tt class="xref py py-meth docutils literal"><span class="pre">default()</span></tt></a> method with another method that returns a serializable object
for <tt class="docutils literal"><span class="pre">o</span></tt> if possible, otherwise it should call the superclass implementation
(to raise <a class="reference internal" href="exceptions.html#exceptions.TypeError" title="exceptions.TypeError"><tt class="xref py py-exc docutils literal"><span class="pre">TypeError</span></tt></a>).</p>
<p>If <em>skipkeys</em> is <tt class="docutils literal"><span class="pre">False</span></tt> (the default), then it is a <a class="reference internal" href="exceptions.html#exceptions.TypeError" title="exceptions.TypeError"><tt class="xref py py-exc docutils literal"><span class="pre">TypeError</span></tt></a> to
attempt encoding of keys that are not str, int, long, float or None. If
<em>skipkeys</em> is <tt class="docutils literal"><span class="pre">True</span></tt>, such items are simply skipped.</p>
<p>If <em>ensure_ascii</em> is <tt class="docutils literal"><span class="pre">True</span></tt> (the default), all non-ASCII characters in the
output are escaped with <tt class="docutils literal"><span class="pre">\uXXXX</span></tt> sequences, and the results are
<a class="reference internal" href="functions.html#str" title="str"><tt class="xref py py-class docutils literal"><span class="pre">str</span></tt></a> instances consisting of ASCII characters only. If
<em>ensure_ascii</em> is <tt class="docutils literal"><span class="pre">False</span></tt>, a result may be a <a class="reference internal" href="functions.html#unicode" title="unicode"><tt class="xref py py-class docutils literal"><span class="pre">unicode</span></tt></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 <tt class="docutils literal"><span class="pre">True</span></tt> (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"><tt class="xref py py-exc docutils literal"><span class="pre">OverflowError</span></tt></a>).
Otherwise, no such check takes place.</p>
<p>If <em>allow_nan</em> is <tt class="docutils literal"><span class="pre">True</span></tt> (the default), then <tt class="docutils literal"><span class="pre">NaN</span></tt>, <tt class="docutils literal"><span class="pre">Infinity</span></tt>, and
<tt class="docutils literal"><span class="pre">-Infinity</span></tt> 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"><tt class="xref py py-exc docutils literal"><span class="pre">ValueError</span></tt></a> to encode
such floats.</p>
<p>If <em>sort_keys</em> is <tt class="docutils literal"><span class="pre">True</span></tt> (default <tt class="docutils literal"><span class="pre">False</span></tt>), 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 <tt class="docutils literal"><span class="pre">None</span></tt> 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. <tt class="docutils literal"><span class="pre">None</span></tt> 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 <tt class="docutils literal"><span class="pre">',</span> <span class="pre">'</span></tt>, the output might include
trailing whitespace when <em>indent</em> is specified. You can use
<tt class="docutils literal"><span class="pre">separators=(',',</span> <span class="pre">':</span> <span class="pre">')</span></tt> to avoid this.</p>
</div>
<p>If specified, <em>separators</em> should be an <tt class="docutils literal"><span class="pre">(item_separator,</span> <span class="pre">key_separator)</span></tt>
tuple. The default is <tt class="docutils literal"><span class="pre">(',</span> <span class="pre">',</span> <span class="pre">':</span> <span class="pre">')</span></tt>. To get the most compact JSON
representation, you should specify <tt class="docutils literal"><span class="pre">(',',</span> <span class="pre">':')</span></tt> to eliminate whitespace.</p>
<p>If specified, <em>default</em> is 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"><tt class="xref py py-exc docutils literal"><span class="pre">TypeError</span></tt></a>.</p>
<p>If <em>encoding</em> is not <tt class="docutils literal"><span class="pre">None</span></tt>, 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">
<tt class="descname">default</tt><big>(</big><em>o</em><big>)</big><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"><tt class="xref py py-exc docutils literal"><span class="pre">TypeError</span></tt></a>).</p>
<p>For example, to support arbitrary iterators, you could implement default
like this:</p>
<div class="highlight-python"><div class="highlight"><pre><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="c"># 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">
<tt class="descname">encode</tt><big>(</big><em>o</em><big>)</big><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"><div class="highlight"><pre><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="s">"foo"</span><span class="p">:</span> <span class="p">[</span><span class="s">"bar"</span><span class="p">,</span> <span class="s">"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">
<tt class="descname">iterencode</tt><big>(</big><em>o</em><big>)</big><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"><div class="highlight"><pre><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">
<h2>18.2.3. Standard Compliance<a class="headerlink" href="#standard-compliance" title="Permalink to this headline">¶</a></h2>
<p>The JSON format is specified by <span class="target" id="index-1"></span><a class="rfc reference external" href="http://tools.ietf.org/html/rfc4627.html"><strong>RFC 4627</strong></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"><tt class="xref py py-class docutils literal"><span class="pre">JSONEncoder</span></tt></a> and <a class="reference internal" href="#json.JSONDecoder" title="json.JSONDecoder"><tt class="xref py py-class docutils literal"><span class="pre">JSONDecoder</span></tt></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>Top-level non-object, non-array values are accepted and output;</li>
<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 recommends that JSON be represented using either UTF-8, UTF-16, or
UTF-32, with UTF-8 being the default. 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>The RFC also non-normatively describes a limited encoding detection technique
for JSON texts; this module’s deserializer does not implement this or any other
kind of encoding detection.</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>
</div>
<div class="section" id="top-level-non-object-non-array-values">
<h3>18.2.3.2. 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 RFC specifies 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"><tt class="xref py py-class docutils literal"><span class="pre">dict</span></tt></a> or <a class="reference internal" href="functions.html#list" title="list"><tt class="xref py py-class docutils literal"><span class="pre">list</span></tt></a>). This module’s
deserializer also accepts input texts consisting solely of a
JSON null, boolean, number, or string value:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">just_a_json_string</span> <span class="o">=</span> <span class="s">'"spam and eggs"'</span> <span class="c"># Not by itself a valid JSON text</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">just_a_json_string</span><span class="p">)</span>
<span class="go">u'spam and eggs'</span>
</pre></div>
</div>
<p>This module itself does not include a way to request that such input texts be
regarded as illegal. Likewise, this module’s serializer also accepts single
Python <a class="reference internal" href="constants.html#None" title="None"><tt class="xref py py-data docutils literal"><span class="pre">None</span></tt></a>, <a class="reference internal" href="functions.html#bool" title="bool"><tt class="xref py py-class docutils literal"><span class="pre">bool</span></tt></a>, numeric, and <a class="reference internal" href="functions.html#str" title="str"><tt class="xref py py-class docutils literal"><span class="pre">str</span></tt></a>
values as input and will generate output texts consisting solely of a top-level
JSON null, boolean, number, or string value without raising an exception:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">neither_a_list_nor_a_dict</span> <span class="o">=</span> <span class="s">u"spam and eggs"</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="n">neither_a_list_nor_a_dict</span><span class="p">)</span> <span class="c"># The result is not a valid JSON text</span>
<span class="go">'"spam and eggs"'</span>
</pre></div>
</div>
<p>This module’s serializer does not itself include a way to enforce the
aforementioned constraint.</p>
</div>
<div class="section" id="infinite-and-nan-number-values">
<h3>18.2.3.3. 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 <tt class="docutils literal"><span class="pre">Infinity</span></tt>,
<tt class="docutils literal"><span class="pre">-Infinity</span></tt>, and <tt class="docutils literal"><span class="pre">NaN</span></tt> as if they were valid JSON number literal values:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="c"># 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="s">'-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="s">'nan'</span><span class="p">))</span>
<span class="go">'NaN'</span>
<span class="gp">>>> </span><span class="c"># 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="s">'-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="s">'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>18.2.3.4. 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 specify 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"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">weird_json</span> <span class="o">=</span> <span class="s">'{"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>
</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="#">18.2. <tt class="docutils literal"><span class="pre">json</span></tt> — 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">18.2.3. Standard Compliance</a><ul>
<li><a class="reference internal" href="#character-encodings">18.2.3.1. Character Encodings</a></li>
<li><a class="reference internal" href="#top-level-non-object-non-array-values">18.2.3.2. Top-level Non-Object, Non-Array Values</a></li>
<li><a class="reference internal" href="#infinite-and-nan-number-values">18.2.3.3. Infinite and NaN Number Values</a></li>
<li><a class="reference internal" href="#repeated-names-within-an-object">18.2.3.4. Repeated Names Within an Object</a></li>
</ul>
</li>
</ul>
</li>
</ul>
<h4>Previous topic</h4>
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title="previous chapter">18.1.11. <tt class="docutils literal"><span class="pre">email</span></tt>: Examples</a></p>
<h4>Next topic</h4>
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