1[section boost/python/to_python_converter.hpp] 2[section Introduction] 3`to_python_converter` registers a conversion from objects of a given C++ type into a Python object. 4[endsect] 5[section Class template `to_python_converter`] 6`to_python_converter` adds a wrapper around a static member function of its second template parameter, handling low-level details such as insertion into the converter registry. 7 8In the table below, x denotes an object of type T 9[table 10[[Parameter][Requirements][Description]] 11[[T][][The C++ type of the source object in the conversion]] 12[[Conversion][`PyObject* p = Conversion::convert(x)`, 13`if p == 0`, `PyErr_Occurred() != 0`.][A class type whose static member function convert does the real work of the conversion.]] 14[[bool has_get_pytype=false][`PyTypeObject const * p = Conversion::get_pytype()`] 15[Optional member - if Conversion has `get_pytype` member supply `true` for this parameters. If present `get_pytype` is used to document the return type of functions using this conversion. The `get_pytype` may be implemented using the classes and functions from pytype_function.hpp NOTE : For backward compatibility this parameter may be passed after checking if BOOST_PYTHON_SUPPORTS_PY_SIGNATURES is defined (see [link function_invocation_and_creation.function_documentation.boost_python_pytype_function_hpp.example here]).] 16]] 17 18`` 19namespace boost { namespace python 20{ 21 template <class T, class Conversion, bool convertion_has_get_pytype_member=false> 22 struct to_python_converter 23 { 24 to_python_converter(); 25 }; 26}} 27`` 28[section Class template `to_python_converter` constructor] 29``to_python_converter();`` 30[variablelist 31[[Effects][Registers a `to_python` converter which uses `Conversion::convert()` to do its work.]] 32] 33[endsect] 34[endsect] 35[section Example] 36This example presumes that someone has implemented the standard noddy example module from the Python documentation, and placed the corresponding declarations in "noddy.h". Because noddy_NoddyObject is the ultimate trivial extension type, the example is a bit contrived: it wraps a function for which all information is contained in the type of its return value. 37 38In C++: 39`` 40#include <boost/python/reference.hpp> 41#include <boost/python/module.hpp> 42#include "noddy.h" 43 44struct tag {}; 45tag make_tag() { return tag(); } 46 47using namespace boost::python; 48 49struct tag_to_noddy 50{ 51 static PyObject* convert(tag const& x) 52 { 53 return PyObject_New(noddy_NoddyObject, &noddy_NoddyType); 54 } 55 static PyTypeObject const* get_pytype() 56 { 57 return &noddy_NoddyType; 58 } 59}; 60 61BOOST_PYTHON_MODULE(to_python_converter) 62{ 63 def("make_tag", make_tag); 64 to_python_converter<tag, tag_to_noddy, true>(); //"true" because tag_to_noddy has member get_pytype 65} 66`` 67In Python: 68`` 69>>> import to_python_converter 70>>> def always_none(): 71... return None 72... 73>>> def choose_function(x): 74... if (x % 2 != 0): 75... return to_python_converter.make_tag 76... else: 77... return always_none 78... 79>>> a = [ choose_function(x) for x in range(5) ] 80>>> b = [ f() for f in a ] 81>>> type(b[0]) 82<type 'NoneType'> 83>>> type(b[1]) 84<type 'Noddy'> 85>>> type(b[2]) 86<type 'NoneType'> 87>>> type(b[3]) 88<type 'Noddy'> 89`` 90[endsect] 91[endsect] 92