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Code Editor : iter.html

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  <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="c function">
<dt class="sig sig-object c" id="c.PyIter_Check">
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyIter_Check</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><span class="n"><span class="pre">PyObject</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">o</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyIter_Check" title="Permalink to this definition">¶</a><br /></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 <code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code>.</p>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyIter_Next">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><span class="n"><span class="pre">PyObject</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="sig-name descname"><span class="n"><span class="pre">PyIter_Next</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><span class="n"><span class="pre">PyObject</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">o</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyIter_Next" title="Permalink to this definition">¶</a><br /></dt>
<dd><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-default 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="n">NULL</span><span class="p">)</span> <span class="p">{</span>
    <span class="o">/*</span> <span class="n">propagate</span> <span class="n">error</span> <span class="o">*/</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="o">/*</span> <span class="n">do</span> <span class="n">something</span> <span class="k">with</span> <span class="n">item</span> <span class="o">*/</span>
    <span class="o">...</span>
    <span class="o">/*</span> <span class="n">release</span> <span class="n">reference</span> <span class="n">when</span> <span class="n">done</span> <span class="o">*/</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="o">/*</span> <span class="n">propagate</span> <span class="n">error</span> <span class="o">*/</span>
<span class="p">}</span>
<span class="k">else</span> <span class="p">{</span>
    <span class="o">/*</span> <span class="k">continue</span> <span class="n">doing</span> <span class="n">useful</span> <span class="n">work</span> <span class="o">*/</span>
<span class="p">}</span>
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