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<div class="section" id="iterator-protocol">
<span id="iterator"></span><h1>Iterator Protocol<a class="headerlink" href="#iterator-protocol" title="Permalink to this headline">¶</a></h1>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.2.</span></p>
</div>
<p>There are two functions specifically for working with iterators.</p>
<dl class="function">
<dt id="c.PyIter_Check">
int <code class="descname">PyIter_Check</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *o</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyIter_Check" title="Permalink to this definition">¶</a></dt>
<dd><p>Return true if the object <em>o</em> supports the iterator protocol.</p>
<p>This function can return a false positive in the case of old-style
classes because those classes always define a <code class="xref c c-member docutils literal notranslate"><span class="pre">tp_iternext</span></code>
slot with logic that either invokes a <a class="reference internal" href="../library/functions.html#next" title="next"><code class="xref py py-meth docutils literal notranslate"><span class="pre">next()</span></code></a> method or raises
a <a class="reference internal" href="../library/exceptions.html#exceptions.TypeError" title="exceptions.TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>.</p>
</dd></dl>
<dl class="function">
<dt id="c.PyIter_Next">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a>* <code class="descname">PyIter_Next</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *o</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyIter_Next" title="Permalink to this definition">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>Return the next value from the iteration <em>o</em>. The object must be an iterator
(it is up to the caller to check this). If there are no remaining values,
returns <em>NULL</em> with no exception set. If an error occurs while retrieving
the item, returns <em>NULL</em> and passes along the exception.</p>
</dd></dl>
<p>To write a loop which iterates over an iterator, the C code should look
something like this:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">PyObject</span> <span class="o">*</span><span class="n">iterator</span> <span class="o">=</span> <span class="n">PyObject_GetIter</span><span class="p">(</span><span class="n">obj</span><span class="p">);</span>
<span class="n">PyObject</span> <span class="o">*</span><span class="n">item</span><span class="p">;</span>
<span class="k">if</span> <span class="p">(</span><span class="n">iterator</span> <span class="o">==</span> <span class="nb">NULL</span><span class="p">)</span> <span class="p">{</span>
<span class="cm">/* propagate error */</span>
<span class="p">}</span>
<span class="k">while</span> <span class="p">(</span><span class="n">item</span> <span class="o">=</span> <span class="n">PyIter_Next</span><span class="p">(</span><span class="n">iterator</span><span class="p">))</span> <span class="p">{</span>
<span class="cm">/* do something with item */</span>
<span class="p">...</span>
<span class="cm">/* release reference when done */</span>
<span class="n">Py_DECREF</span><span class="p">(</span><span class="n">item</span><span class="p">);</span>
<span class="p">}</span>
<span class="n">Py_DECREF</span><span class="p">(</span><span class="n">iterator</span><span class="p">);</span>
<span class="k">if</span> <span class="p">(</span><span class="n">PyErr_Occurred</span><span class="p">())</span> <span class="p">{</span>
<span class="cm">/* propagate error */</span>
<span class="p">}</span>
<span class="k">else</span> <span class="p">{</span>
<span class="cm">/* continue doing useful work */</span>
<span class="p">}</span>
</pre></div>
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