12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596061626364656667686970717273747576777879808182838485868788899091 |
- [section boost/python/to_python_converter.hpp]
- [section Introduction]
- `to_python_converter` registers a conversion from objects of a given C++ type into a Python object.
- [endsect]
- [section Class template `to_python_converter`]
- `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.
- In the table below, x denotes an object of type T
- [table
- [[Parameter][Requirements][Description]]
- [[T][][The C++ type of the source object in the conversion]]
- [[Conversion][`PyObject* p = Conversion::convert(x)`,
- `if p == 0`, `PyErr_Occurred() != 0`.][A class type whose static member function convert does the real work of the conversion.]]
- [[bool has_get_pytype=false][`PyTypeObject const * p = Conversion::get_pytype()`]
- [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]).]
- ]]
- ``
- namespace boost { namespace python
- {
- template <class T, class Conversion, bool convertion_has_get_pytype_member=false>
- struct to_python_converter
- {
- to_python_converter();
- };
- }}
- ``
- [section Class template `to_python_converter` constructor]
- ``to_python_converter();``
- [variablelist
- [[Effects][Registers a `to_python` converter which uses `Conversion::convert()` to do its work.]]
- ]
- [endsect]
- [endsect]
- [section Example]
- This 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.
- In C++:
- ``
- #include <boost/python/reference.hpp>
- #include <boost/python/module.hpp>
- #include "noddy.h"
- struct tag {};
- tag make_tag() { return tag(); }
- using namespace boost::python;
- struct tag_to_noddy
- {
- static PyObject* convert(tag const& x)
- {
- return PyObject_New(noddy_NoddyObject, &noddy_NoddyType);
- }
- static PyTypeObject const* get_pytype()
- {
- return &noddy_NoddyType;
- }
- };
- BOOST_PYTHON_MODULE(to_python_converter)
- {
- def("make_tag", make_tag);
- to_python_converter<tag, tag_to_noddy, true>(); //"true" because tag_to_noddy has member get_pytype
- }
- ``
- In Python:
- ``
- >>> import to_python_converter
- >>> def always_none():
- ... return None
- ...
- >>> def choose_function(x):
- ... if (x % 2 != 0):
- ... return to_python_converter.make_tag
- ... else:
- ... return always_none
- ...
- >>> a = [ choose_function(x) for x in range(5) ]
- >>> b = [ f() for f in a ]
- >>> type(b[0])
- <type 'NoneType'>
- >>> type(b[1])
- <type 'Noddy'>
- >>> type(b[2])
- <type 'NoneType'>
- >>> type(b[3])
- <type 'Noddy'>
- ``
- [endsect]
- [endsect]
|