...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
<boost/python/call_method.hpp> defines the call_method family of overloaded function templates, used to invoke callable attributes of Python objects from C++.
template <class R, class A1, class A2, ... class An> R call_method(PyObject* self, char const* method, A1 const&, A2 const&, ... An const&)
R
is a pointer type,
reference type, or a complete type with an accessible copy constructor
Invokes self.method(a1, a2, ...an)
in Python, where a1...an
are the arguments to call_method()
, converted to Python objects. For
a complete semantic description, see this page.
The result of the Python call, converted to the C++ type R
.
call_method
is critical
to implementing C++ virtual functions which are overridable in Python,
as shown by the example below.
The following C++ illustrates the use of call_method
in wrapping a class with a virtual function that can be overridden in Python:
C++ Module Definition
#include <boost/python/module.hpp> #include <boost/python/class.hpp> #include <boost/python/call_method.hpp> #include <boost/python/def.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 call_method<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, boost::noncopyable>("Base") .def("class_name", &Base_callback::Base_name) ; }
Python code:
>>> 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