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<title>Boost.Python - <call_method.hpp></title>
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<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../boost.png" border="0"></a></h3>
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<h1 align="center"><a href="../index.html">Boost.Python</a></h1>
<h2 align="center">Header <call_method.hpp></h2>
</td>
</tr>
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<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#functions">Functions</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#call_method-spec">call_method</a></dt>
</dl>
</dd>
<dt><a href="#examples">Example(s)</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p><code><boost/python/call_method.hpp></code> defines the <a href=
"#call_method-spec"><code>call_method</code></a> family of overloaded
function templates, used to invoke callable attributes of Python objects
from C++.</p>
<h2><a name="functions"></a>Functions</h2>
<pre>
<a name=
"call_method-spec">template <class R, class A1, class A2, ... class A<i>n</i>></a>
R call_method(PyObject* self, char const* method, A1 const&, A2 const&, ... A<i>n</i> const&)
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>R</code> is a pointer type, reference type,
or a complete type with an accessible copy constructor</dt>
<dt><b>Effects:</b> Invokes
<code>self.<i>method</i>(a1, a2, ...a<i>n</i>)</code> in
Python, where <code>a1</code>...<code>a<i>n</i></code> are the
arguments to <code>call_method()</code>, converted to Python objects.
For a complete semantic description, see <a href="callbacks.html">this
page</a>.</dt>
<dt><b>Returns:</b> The result of the Python call, converted to the C++
type <code>R</code>.</dt>
<dt><b>Rationale:</b> <code>call_method</code> is critical to
implementing C++ virtual functions which are overridable in Python, as
shown by the example below.</dt>
</dl>
<h2><a name="examples"></a>Example(s)</h2>
The following C++ illustrates the use of <code>call_method</code> in
wrapping a class with a virtual function that can be overridden in
Python:
<h3>C++ Module Definition</h3>
<pre>
#include <boost/python/module.hpp>
#include <boost/python/class.hpp>
#include <boost/utility.hpp>
#include <cstring>
// class to be wrapped
class Base
{
public:
virtual char const* class_name() const { return "Base"; }
virtual ~Base();
};
bool is_base(Base* b)
{
return !std::strcmp(b->class_name(), "Base");
}
// Wrapper code begins here
using namespace boost::python;
// Callback class
class Base_callback : public Base
{
public:
Base_callback(PyObject* self) : m_self(self) {}
char const* class_name() const { return <b>call_method</b><char const*>(m_self, "class_name"); }
char const* Base_name() const { return Base::class_name(); }
private:
PyObject* const m_self;
};
using namespace boost::python;
BOOST_PYTHON_MODULE(my_module)
{
def("is_base", is_base);
class_<Base,Base_callback, noncopyable>("Base")
.def("class_name", &Base_callback::Base_name)
;
}
</pre>
<h3>Python Code</h3>
<pre>
>>> from my_module import *
>>> class Derived(Base):
... def __init__(self):
... Base.__init__(self)
... def class_name(self):
... return self.__class__.__name__
...
>>> is_base(Base()) # calls the class_name() method from C++
1
>>> is_base(Derived())
0
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
13 November, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>© Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002.</i></p>
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