cython_callback_binding.pyx

constraint_handlers = {}

from cpython.ref cimport PyObject

cdef void _call_constraint_presolve_func(cpConstraint *constraint, cpSpace *space):
    global constraint_handlers
    global current_spaces
    py_space = current_spaces[0]
    py_constraint = <object><void *>constraint.data
    constraint_dict = constraint_handlers[py_constraint]
    constraint_dict['pre_solve'](py_constraint, py_space)

cdef class Constraint:
   def __init__(self, args):
        self._constraint = cpConstraint()
        # XXX maybe void* is not necessary if cython recognize cpDataPointer as void*.
        # Because the constraint C struct data contain self, there is no need to store self in the dict
        # Just use self as a key.
        # If "self" cannot be used as a key, use its memory location/pointer: id(self)
        self._constraint.data = <cpDataPointer><void *>self
        global constraint_handlers
        constraint_handlers[self] = {}

   def __dealloc__(self):
        global constraint_handlers
        del constraint_handlers[self]

   property pre_solve:
        def __set__(self, func):
            self._set_py_presolve_handler(func)
            self._constraint.preSolve = _call_constraint_presolve_func

   def _set_py_presolve_handler(self, presolve_func):
        global constraint_handlers
        constraint_handlers[self]['pre_solve'] = presolve_func