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<div class="section" id="python-types">
<h1>Python types<a class="headerlink" href="#python-types" title="Permalink to this headline">¶</a></h1>
<div class="section" id="available-wrappers">
<h2>Available wrappers<a class="headerlink" href="#available-wrappers" title="Permalink to this headline">¶</a></h2>
<p>All major Python types are available as thin C++ wrapper classes. These
can also be used as function parameters – see <a class="reference internal" href="../functions.html#python-objects-as-args"><span class="std std-ref">Python objects as arguments</span></a>.</p>
<p>Available types include <a class="reference internal" href="../../reference.html#_CPPv26handle" title="handle"><code class="xref cpp cpp-class docutils literal"><span class="pre">handle</span></code></a>, <a class="reference internal" href="../../reference.html#_CPPv26object" title="object"><code class="xref cpp cpp-class docutils literal"><span class="pre">object</span></code></a>, <code class="xref cpp cpp-class docutils literal"><span class="pre">bool_</span></code>,
<code class="xref cpp cpp-class docutils literal"><span class="pre">int_</span></code>, <code class="xref cpp cpp-class docutils literal"><span class="pre">float_</span></code>, <code class="xref cpp cpp-class docutils literal"><span class="pre">str</span></code>, <code class="xref cpp cpp-class docutils literal"><span class="pre">bytes</span></code>, <code class="xref cpp cpp-class docutils literal"><span class="pre">tuple</span></code>,
<code class="xref cpp cpp-class docutils literal"><span class="pre">list</span></code>, <code class="xref cpp cpp-class docutils literal"><span class="pre">dict</span></code>, <code class="xref cpp cpp-class docutils literal"><span class="pre">slice</span></code>, <code class="xref cpp cpp-class docutils literal"><span class="pre">none</span></code>, <code class="xref cpp cpp-class docutils literal"><span class="pre">capsule</span></code>,
<code class="xref cpp cpp-class docutils literal"><span class="pre">iterable</span></code>, <code class="xref cpp cpp-class docutils literal"><span class="pre">iterator</span></code>, <code class="xref cpp cpp-class docutils literal"><span class="pre">function</span></code>, <code class="xref cpp cpp-class docutils literal"><span class="pre">buffer</span></code>,
<code class="xref cpp cpp-class docutils literal"><span class="pre">array</span></code>, and <code class="xref cpp cpp-class docutils literal"><span class="pre">array_t</span></code>.</p>
</div>
<div class="section" id="casting-back-and-forth">
<h2>Casting back and forth<a class="headerlink" href="#casting-back-and-forth" title="Permalink to this headline">¶</a></h2>
<p>In this kind of mixed code, it is often necessary to convert arbitrary C++
types to Python, which can be done using <code class="xref cpp cpp-func docutils literal"><span class="pre">py::cast()</span></code>:</p>
<div class="highlight-cpp"><div class="highlight"><pre><span></span><span class="n">MyClass</span> <span class="o">*</span><span class="n">cls</span> <span class="o">=</span> <span class="p">..;</span>
<span class="n">py</span><span class="o">::</span><span class="n">object</span> <span class="n">obj</span> <span class="o">=</span> <span class="n">py</span><span class="o">::</span><span class="n">cast</span><span class="p">(</span><span class="n">cls</span><span class="p">);</span>
</pre></div>
</div>
<p>The reverse direction uses the following syntax:</p>
<div class="highlight-cpp"><div class="highlight"><pre><span></span><span class="n">py</span><span class="o">::</span><span class="n">object</span> <span class="n">obj</span> <span class="o">=</span> <span class="p">...;</span>
<span class="n">MyClass</span> <span class="o">*</span><span class="n">cls</span> <span class="o">=</span> <span class="n">obj</span><span class="p">.</span><span class="n">cast</span><span class="o"><</span><span class="n">MyClass</span> <span class="o">*></span><span class="p">();</span>
</pre></div>
</div>
<p>When conversion fails, both directions throw the exception <code class="xref cpp cpp-class docutils literal"><span class="pre">cast_error</span></code>.</p>
</div>
<div class="section" id="calling-python-functions">
<h2>Calling Python functions<a class="headerlink" href="#calling-python-functions" title="Permalink to this headline">¶</a></h2>
<p>It is also possible to call python functions via <code class="docutils literal"><span class="pre">operator()</span></code>.</p>
<div class="highlight-cpp"><div class="highlight"><pre><span></span><span class="n">py</span><span class="o">::</span><span class="n">function</span> <span class="n">f</span> <span class="o">=</span> <span class="o"><</span><span class="p">...</span><span class="o">></span><span class="p">;</span>
<span class="n">py</span><span class="o">::</span><span class="n">object</span> <span class="n">result_py</span> <span class="o">=</span> <span class="n">f</span><span class="p">(</span><span class="mi">1234</span><span class="p">,</span> <span class="s">"hello"</span><span class="p">,</span> <span class="n">some_instance</span><span class="p">);</span>
<span class="n">MyClass</span> <span class="o">&</span><span class="n">result</span> <span class="o">=</span> <span class="n">result_py</span><span class="p">.</span><span class="n">cast</span><span class="o"><</span><span class="n">MyClass</span><span class="o">></span><span class="p">();</span>
</pre></div>
</div>
<p>Keyword arguments are also supported. In Python, there is the usual call syntax:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">f</span><span class="p">(</span><span class="n">number</span><span class="p">,</span> <span class="n">say</span><span class="p">,</span> <span class="n">to</span><span class="p">):</span>
<span class="o">...</span> <span class="c1"># function code</span>
<span class="n">f</span><span class="p">(</span><span class="mi">1234</span><span class="p">,</span> <span class="n">say</span><span class="o">=</span><span class="s2">"hello"</span><span class="p">,</span> <span class="n">to</span><span class="o">=</span><span class="n">some_instance</span><span class="p">)</span> <span class="c1"># keyword call in Python</span>
</pre></div>
</div>
<p>In C++, the same call can be made using:</p>
<div class="highlight-cpp"><div class="highlight"><pre><span></span><span class="k">using</span> <span class="n">pybind11</span><span class="o">::</span><span class="n">literals</span><span class="p">;</span> <span class="c1">// to bring in the `_a` literal</span>
<span class="n">f</span><span class="p">(</span><span class="mi">1234</span><span class="p">,</span> <span class="s">"say"</span><span class="n">_a</span><span class="o">=</span><span class="s">"hello"</span><span class="p">,</span> <span class="s">"to"</span><span class="n">_a</span><span class="o">=</span><span class="n">some_instance</span><span class="p">);</span> <span class="c1">// keyword call in C++</span>
</pre></div>
</div>
<p>Unpacking of <code class="docutils literal"><span class="pre">*args</span></code> and <code class="docutils literal"><span class="pre">**kwargs</span></code> is also possible and can be mixed with
other arguments:</p>
<div class="highlight-cpp"><div class="highlight"><pre><span></span><span class="c1">// * unpacking</span>
<span class="n">py</span><span class="o">::</span><span class="n">tuple</span> <span class="n">args</span> <span class="o">=</span> <span class="n">py</span><span class="o">::</span><span class="n">make_tuple</span><span class="p">(</span><span class="mi">1234</span><span class="p">,</span> <span class="s">"hello"</span><span class="p">,</span> <span class="n">some_instance</span><span class="p">);</span>
<span class="n">f</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">);</span>
<span class="c1">// ** unpacking</span>
<span class="n">py</span><span class="o">::</span><span class="n">dict</span> <span class="n">kwargs</span> <span class="o">=</span> <span class="n">py</span><span class="o">::</span><span class="n">dict</span><span class="p">(</span><span class="s">"number"</span><span class="n">_a</span><span class="o">=</span><span class="mi">1234</span><span class="p">,</span> <span class="s">"say"</span><span class="n">_a</span><span class="o">=</span><span class="s">"hello"</span><span class="p">,</span> <span class="s">"to"</span><span class="n">_a</span><span class="o">=</span><span class="n">some_instance</span><span class="p">);</span>
<span class="n">f</span><span class="p">(</span><span class="o">**</span><span class="n">kwargs</span><span class="p">);</span>
<span class="c1">// mixed keywords, * and ** unpacking</span>
<span class="n">py</span><span class="o">::</span><span class="n">tuple</span> <span class="n">args</span> <span class="o">=</span> <span class="n">py</span><span class="o">::</span><span class="n">make_tuple</span><span class="p">(</span><span class="mi">1234</span><span class="p">);</span>
<span class="n">py</span><span class="o">::</span><span class="n">dict</span> <span class="n">kwargs</span> <span class="o">=</span> <span class="n">py</span><span class="o">::</span><span class="n">dict</span><span class="p">(</span><span class="s">"to"</span><span class="n">_a</span><span class="o">=</span><span class="n">some_instance</span><span class="p">);</span>
<span class="n">f</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="s">"say"</span><span class="n">_a</span><span class="o">=</span><span class="s">"hello"</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">);</span>
</pre></div>
</div>
<p>Generalized unpacking according to <a class="reference external" href="https://www.python.org/dev/peps/pep-0448/">PEP448</a> is also supported:</p>
<div class="highlight-cpp"><div class="highlight"><pre><span></span><span class="n">py</span><span class="o">::</span><span class="n">dict</span> <span class="n">kwargs1</span> <span class="o">=</span> <span class="n">py</span><span class="o">::</span><span class="n">dict</span><span class="p">(</span><span class="s">"number"</span><span class="n">_a</span><span class="o">=</span><span class="mi">1234</span><span class="p">);</span>
<span class="n">py</span><span class="o">::</span><span class="n">dict</span> <span class="n">kwargs2</span> <span class="o">=</span> <span class="n">py</span><span class="o">::</span><span class="n">dict</span><span class="p">(</span><span class="s">"to"</span><span class="n">_a</span><span class="o">=</span><span class="n">some_instance</span><span class="p">);</span>
<span class="n">f</span><span class="p">(</span><span class="o">**</span><span class="n">kwargs1</span><span class="p">,</span> <span class="s">"say"</span><span class="n">_a</span><span class="o">=</span><span class="s">"hello"</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs2</span><span class="p">);</span>
</pre></div>
</div>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last">The file <code class="file docutils literal"><span class="pre">tests/test_python_types.cpp</span></code> contains a complete
example that demonstrates passing native Python types in more detail. The
file <code class="file docutils literal"><span class="pre">tests/test_callbacks.cpp</span></code> presents a few examples of calling
Python functions from C++, including keywords arguments and unpacking.</p>
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