>> gmpy uses C extension, it's not using ctypes. <<

    import ctypes
    from ctypes.util import find_library

 	_libgmp = ctypes.CDLL(find_library("gmp"))

 	class mpz_t_struct(ctypes.Structure):
 	_fields_ = [("mp_alloc", ctypes.c_int),
 	("mp_size", ctypes.c_int),
 	("mp_d", ctypes.c_void_p)]