C++ this pointer equivalent in Python ctypes

I'm calling a C dll from Python using ctypes and having some trouble passing the correct parameters to the IBSU_RegisterCallbacks function, defined below.

int WINAPI IBSU_RegisterCallbacks
    (const int         handle, 
     const IBSU_Events event, 
     void             *pCallbackFunction,
     void             *pContext);

It describes the final parameter as:

/* pContext Pointer to user context that will be passed to callback function.*/

A working C++ example calls the function like this:

RegisterCallbacks(0, 1, OnCallback, this);

So far in Python I have the below code (relevant section shown only), which crashes Python (no traceback) shortly after the event is triggered and callback run! is printed.

from ctypes import *

class IBSU(object):
    _dll = WinDLL('ibsu.dll')

    _C_CALLBACK = CFUNCTYPE(
        None,        
        c_int,                                         # device handle
        c_void_p)                                      # user context

    _register_callbacks = _dll.IBSU_RegisterCallbacks
    _register_callbacks.restype = c_int
    _register_callbacks.argtypes = (c_int,             # device handle
                                    c_int,             # event type
                                    c_void_p,          # callback function
                                    c_void_p)          # user context

    def _get_c_callback(self):
        def callback(handle,                           # device handle
                     p_context):                       # user context
            print 'callback run!'
        return self._C_CALLBACK(callback) 

    def register_callbacks(self):
        # keep ref to prevent garbage collection
        self._c_callback = self._get_c_callback()

        self._register_callbacks(0,                    # device handle
                                 1,                    # event type
                                 self._c_callback,     # callback function
                                 c_void_p())           # user context

What is the equivalent to this in my Python class that I can send instead of just c_void_p()?