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- [section boost/python/call_method.hpp]
- [section Introduction]
- <boost/python/call_method.hpp> defines the call_method family of overloaded function templates, used to invoke callable attributes of Python objects from C++.
- [endsect]
- [section Function `call_method`]
- ``
- template <class R, class A1, class A2, ... class An>
- R call_method(PyObject* self, char const* method, A1 const&, A2 const&, ... An const&)
- ``
- [variablelist
- [[Requires][`R` is a pointer type, reference type, or a complete type with an accessible copy constructor]]
- [[Effects][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.]]
- [[Returns][The result of the Python call, converted to the C++ type `R`.]]
- [[Rationale][`call_method` is critical to implementing C++ virtual functions which are overridable in Python, as shown by the example below.]]
- ]
- [endsect]
- [section Example]
- 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/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, 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
- ``
- [endsect]
- [endsect]
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