...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
make_function() and make_constructor() are the functions used internally by def() and class_<>::def() to produce Python callable objects which wrap C++ functions and member functions.
template <class F> object make_function(F f) template <class F, class Policies> object make_function(F f, Policies const& policies) template <class F, class Policies, class KeywordsOrSignature> object make_function(F f, Policies const& policies, KeywordsOrSignature const& ks) template <class F, class Policies, class Keywords, class Signature> object make_function(F f, Policies const& policies, Keywords const& kw, Signature const& sig)
F is a function pointer or member function pointer type. If policies are supplied, it must be a model of CallPolicies. If kewords are supplied, it must be the result of a keyword-expression specifying no more arguments than the arity of f.
Creates a Python callable object which, when called from Python, converts its arguments to C++ and calls f. If F is a pointer-to-member-function type, the target object of the function call (*this) will be taken from the first Python argument, and subsequent Python arguments will be used as the arguments to f.
An instance of object which holds the new Python callable object.
An argument of pointer type may be 0 if None is passed from Python. An argument type which is a constant reference may refer to a temporary which was created from the Python object for just the duration of the call to the wrapped function, for example a std::vector conjured up by the conversion process from a Python list. Use a non-const reference argument when a persistent lvalue is required.
template <class F> object make_constructor(F f) template <class F, class Policies> object make_constructor(F f, Policies const& policies) template <class F, class Policies, class KeywordsOrSignature> object make_constructor(F f, Policies const& policies, KeywordsOrSignature const& ks) template <class F, class Policies, class Keywords, class Signature> object make_constructor(F f, Policies const& policies, Keywords const& kw, Signature const& sig)
F is a function pointer type. If policies are supplied, it must be a model of CallPolicies. If kewords are supplied, it must be the result of a keyword-expression specifying no more arguments than the arity of f.
Creates a Python callable object which, when called from Python, converts its arguments to C++ and calls f.
An instance of object which holds the new Python callable object.
C++ function exposed below returns a callable object wrapping one of two functions.
#include <boost/python/make_function.hpp> #include <boost/python/module.hpp> char const* foo() { return "foo"; } char const* bar() { return "bar"; } using namespace boost::python; object choose_function(bool selector) { if (selector) return boost::python::make_function(foo); else return boost::python::make_function(bar); } BOOST_PYTHON_MODULE(make_function_test) { def("choose_function", choose_function); }
It can be used this way in Python:
>>> from make_function_test import * >>> f = choose_function(1) >>> g = choose_function(0) >>> f() 'foo' >>> g() 'bar'