text: #! /usr/bin/env python
  
  import sys
  
  import pybindgen
  from pybindgen import ReturnValue, Parameter, Module, Function, FileCodeSink
  from pybindgen import CppMethod, CppConstructor, CppClass, Enum
  from pybindgen.typehandlers.base import ForwardWrapperBase
  
  
  class VisitorParam(Parameter):
  
      DIRECTIONS = [Parameter.DIRECTION_IN]
      CTYPES = ['Visitor']
  
      def convert_python_to_c(self, wrapper):
          assert isinstance(wrapper, ForwardWrapperBase)
  
          py_cb = wrapper.declarations.declare_variable("PyObject*", self.name)
          wrapper.parse_params.add_parameter('O', ['&'+py_cb], self.name)
  
          wrapper.before_call.write_error_check("!PyCallable_Check(%s)" % py_cb,
                                                """PyErr_SetString(PyExc_TypeError, "visitor parameter must be callable");""")
          wrapper.call_params.append("_wrap_Visit")
          wrapper.before_call.write_code("Py_INCREF(%s);" % py_cb)
          wrapper.before_call.add_cleanup_code("Py_DECREF(%s);" % py_cb)
          wrapper.call_params.append(py_cb)
  
  
      def convert_c_to_python(self, wrapper):
          raise NotImplementedError
  
  
  
  def my_module_gen(out_file):
  
      mod = Module('c')
      mod.add_include('"c.h"')
  
      mod.header.writeln("""void _wrap_Visit(int value, void *data);""")
      mod.body.writeln("""
  void _wrap_Visit(int value, void *data)
  {
      PyObject *callback = (PyObject*) data;
      PyObject_CallFunction(callback, (char*) "i", value);
  }
  """)
  
      mod.add_function("visit", None, [Parameter.new("Visitor", "visitor")]
                       # the 'data' parameter is inserted automatically
                       # by the custom callback type handler
                       )
  
      mod.generate(FileCodeSink(out_file))
  
  if __name__ == '__main__':
      my_module_gen(sys.stdout)
  