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142 lines
4.2 KiB
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<link rel="stylesheet" type="text/css" href="../boost.css">
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<title>Boost.Python - <call_method.hpp></title>
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</head>
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<body link="#0000ff" vlink="#800080">
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<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
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"header">
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<tr>
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<td valign="top" width="300">
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<h3><a href="../../../../index.htm"><img height="86" width="277" alt=
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"C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
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</td>
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<td valign="top">
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<h1 align="center">Boost.Python</h1>
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<h2 align="center">Header <call_method.hpp></h2>
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</td>
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</tr>
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</table>
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<hr>
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<h2>Contents</h2>
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<dl class="page-index">
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<dt><a href="#introduction">Introduction</a></dt>
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<dt><a href="#functions">Functions</a></dt>
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<dl class="page-index">
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<dt><a href="#call_method-spec">call_method</a></dt>
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</dl>
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<dt><a href="#examples">Example(s)</a></dt>
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</dl>
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<hr>
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<h2><a name="introduction"></a>Introduction</h2>
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<p>
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<code><boost/python/call_method.hpp></code> defines the <a
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href="#call_method-spec"><code>call_method</code></a> family of overloaded function
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templates, used to invoke callable attributes of Python objects from C++.
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<h2><a name="functions"></a>Functions</h2>
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<pre>
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<a name="call_method-spec">template <class R, class A1, class A2, ... class A<i>n</i>></a>
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R call_method(PyObject* self, char const* method, A1 const&, A2 const&, ... A<i>n</i> const&)
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</pre>
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<dl class="function-semantics">
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<dt><b>Requires:</b> <code>R</code> is a pointer type, reference
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type, or a complete type with an accessible copy constructor</dt>
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<dt><b>Effects:</b> Invokes <code>self.<i>method</i>(a1, a2, ...a<i>n</i>)</code> in
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Python, where <code>a1</code>...<code>a<i>n</i></code> are the arguments to
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<code>call_method()</code>, converted to Python objects. For a
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complete semantic description, see <a href="callbacks.html">this
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page</a>.
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<dt><b>Returns:</b> The result of the Python call, converted to the
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C++ type <code>R</code>.</dt>
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</dt>
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<dt><b>Rationale:</b> <code>call_method</code> is critical to
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implementing C++ virtual functions which are overridable in Python,
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as shown by the example below.
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</dt>
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</dl>
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<h2><a name="examples"></a>Example(s)</h2>
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The following C++ illustrates the use of <code>call_method</code> in
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wrapping a class with a virtual function that can be overridden in
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Python:
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<h3>C++ Module Definition</h3>
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<pre>
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#include <boost/python/module.hpp>
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#include <boost/python/class.hpp>
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#include <boost/utility.hpp>
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#include <cstring>
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// class to be wrapped
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class Base
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{
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public:
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virtual char const* class_name() const { return "Base"; }
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virtual ~Base();
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};
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bool is_base(Base* b)
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{
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return !std::strcmp(b->class_name(), "Base");
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}
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// Wrapper code begins here
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using namespace boost::python;
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// Callback class
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class Base_callback : public Base
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{
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public:
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Base_callback(PyObject* self) : m_self(self) {}
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char const* class_name() const { return <b>call_method</b>(m_self, "class_name"); }
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char const* Base_name() const { return Base::class_name(); }
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private:
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PyObject* m_self;
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};
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using namespace boost::python;
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BOOST_PYTHON_MODULE_INIT(my_module)
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{
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module("my_module")
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.def("is_base", is_base)
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.add(
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class_<Base,Base_callback, noncopyable>("Base")
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.def("class_name", Base_callback::Base_name);
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)
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;
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}
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</pre>
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<h3>Python Code</h3>
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<pre>
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>>> from my_module import *
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>>> class Derived(Base):
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... def __init__(self):
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... Base.__init__(self)
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... def class_name(self):
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... return self.__class__.__name__
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...
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>>> is_base(Base()) # calls the class_name() method from C++
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1
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>>> is_base(Derived())
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0
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</pre>
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<p>Revised
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<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
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10 May, 2002
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<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
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</p>
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<p><i>© Copyright <a href="../../../../people/dave_abrahams.htm">Dave Abrahams</a>
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2002. All Rights Reserved.</i></p>
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</body>
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</html>
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