How do you pass a void * back and forth to a shared library in python using ctypes?

Question

I believe the basic process is:

from ctypes import *

LEAP = ctypes.CDLL('leap.dylib')

leap_controller = LEAP.leap_controller
leap_controller.res_type = c_void_p

leap_controller_dispose = LEAP.leap_controller_dispose
leap_controller_dispose.argtype = [c_void_p]

However, when I invoke this code it mangles the void * pointer. Debugging from the associated C code, I get:

doug:test doug$ python test.py
Controller init!
returning: 0x7fcf9a0022c0
Created controller

Controller dispose!
argument: 0xffffffff9a0022c0
Segmentation fault: 11

Obviously the free() call fails because the pointer isn't right.

I've tried a couple of variations on this, for example, defining a structure, like:

class LEAP_CONTROLLER(Structure):
  _fields_ = [
      ("data", c_void_p)
  ]

leap_controller = LEAP.leap_controller
leap_controller.res_type = POINTER(LEAP_CONTROLLER)

leap_controller_dispose = LEAP.leap_controller_dispose
leap_controller_dispose.argtype = [POINTER(LEAP_CONTROLLER)]

...but the result always seems to be the same.

Python reads the pointer, but only keeps 32 bits worth of data, and returns a broken pointer with the remaining bits all 1.

Both of the binaries are 64 bit:

Non-fat file: /usr/local/bin/python is architecture: x86_64
Non-fat file: ../../dll/libcleap.dylib is architecture: x86_64

I saw this ancient issue, here: http://bugs.python.org/issue1703286

...but it's marked as resolved.

A few other random mailing this threads seem to mention ctypes 'truncating 64-bit pointers to 32-bit', but people all seem to have magically resolved their issues without doing anything ('it works now') or gotten no answer to their questions.

Anyone know what I'm doing wrong?

Answer 1

Answer as per the comments; this was a typo in my code.

 Per the docs, it's argtypes and restype, not argtype and res_type. –  eryksun Oct 4 at 2:31