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<section id="objects-for-type-hinting">
<span id="typehintobjects"></span><h1>Objects for Type Hinting<a class="headerlink" href="#objects-for-type-hinting" title="Link to this heading">¶</a></h1>
<p>Various built-in types for type hinting are provided. Currently,
two types exist – <a class="reference internal" href="../library/stdtypes.html#types-genericalias"><span class="std std-ref">GenericAlias</span></a> and
<a class="reference internal" href="../library/stdtypes.html#types-union"><span class="std std-ref">Union</span></a>. Only <code class="docutils literal notranslate"><span class="pre">GenericAlias</span></code> is exposed to C.</p>
<dl class="c function">
<dt class="sig sig-object c" id="c.Py_GenericAlias">
<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">Py_GenericAlias</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">origin</span></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">args</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_GenericAlias" title="Link to this definition">¶</a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a> since version 3.9.</em><p>Create a <a class="reference internal" href="../library/stdtypes.html#types-genericalias"><span class="std std-ref">GenericAlias</span></a> object.
Equivalent to calling the Python class
<a class="reference internal" href="../library/types.html#types.GenericAlias" title="types.GenericAlias"><code class="xref py py-class docutils literal notranslate"><span class="pre">types.GenericAlias</span></code></a>. The <em>origin</em> and <em>args</em> arguments set the
<code class="docutils literal notranslate"><span class="pre">GenericAlias</span></code>‘s <code class="docutils literal notranslate"><span class="pre">__origin__</span></code> and <code class="docutils literal notranslate"><span class="pre">__args__</span></code> attributes respectively.
<em>origin</em> should be a <span class="c-expr sig sig-inline c"><a class="reference internal" href="type.html#c.PyTypeObject" title="PyTypeObject"><span class="n">PyTypeObject</span></a><span class="p">*</span></span>, and <em>args</em> can be a
<span class="c-expr sig sig-inline c"><a class="reference internal" href="tuple.html#c.PyTupleObject" title="PyTupleObject"><span class="n">PyTupleObject</span></a><span class="p">*</span></span> or any <code class="docutils literal notranslate"><span class="pre">PyObject*</span></code>. If <em>args</em> passed is
not a tuple, a 1-tuple is automatically constructed and <code class="docutils literal notranslate"><span class="pre">__args__</span></code> is set
to <code class="docutils literal notranslate"><span class="pre">(args,)</span></code>.
Minimal checking is done for the arguments, so the function will succeed even
if <em>origin</em> is not a type.
The <code class="docutils literal notranslate"><span class="pre">GenericAlias</span></code>‘s <code class="docutils literal notranslate"><span class="pre">__parameters__</span></code> attribute is constructed lazily
from <code class="docutils literal notranslate"><span class="pre">__args__</span></code>. On failure, an exception is raised and <code class="docutils literal notranslate"><span class="pre">NULL</span></code> is
returned.</p>
<p>Here’s an example of how to make an extension type generic:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="p">...</span>
<span class="k">static</span><span class="w"> </span><span class="n">PyMethodDef</span><span class="w"> </span><span class="n">my_obj_methods</span><span class="p">[]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="c1">// Other methods.</span>
<span class="w"> </span><span class="p">...</span>
<span class="w"> </span><span class="p">{</span><span class="s">"__class_getitem__"</span><span class="p">,</span><span class="w"> </span><span class="n">Py_GenericAlias</span><span class="p">,</span><span class="w"> </span><span class="n">METH_O</span><span class="o">|</span><span class="n">METH_CLASS</span><span class="p">,</span><span class="w"> </span><span class="s">"See PEP 585"</span><span class="p">}</span>
<span class="w"> </span><span class="p">...</span>
<span class="p">}</span>
</pre></div>
</div>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<p>The data model method <a class="reference internal" href="../reference/datamodel.html#object.__class_getitem__" title="object.__class_getitem__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__class_getitem__()</span></code></a>.</p>
</div>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.9.</span></p>
</div>
</dd></dl>
<dl class="c var">
<dt class="sig sig-object c" id="c.Py_GenericAliasType">
<a class="reference internal" href="type.html#c.PyTypeObject" title="PyTypeObject"><span class="n"><span class="pre">PyTypeObject</span></span></a><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">Py_GenericAliasType</span></span></span><a class="headerlink" href="#c.Py_GenericAliasType" title="Link to this definition">¶</a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a> since version 3.9.</em><p>The C type of the object returned by <a class="reference internal" href="#c.Py_GenericAlias" title="Py_GenericAlias"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_GenericAlias()</span></code></a>. Equivalent to
<a class="reference internal" href="../library/types.html#types.GenericAlias" title="types.GenericAlias"><code class="xref py py-class docutils literal notranslate"><span class="pre">types.GenericAlias</span></code></a> in Python.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.9.</span></p>
</div>
</dd></dl>
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