Python 2.5 (r25:51908, Nov 24 2006, 11:03:50)
[GCC 3.4.4 20050721 (Red Hat 3.4.4-2)] on linux2
>>> from ctypes import *
>>> c_int(2**31).value
-2147483648
>>> c_long(2**32-1).value
-1

In a 64-bit build, the situation is even worse:

>>> c_int(int(2**32)).value
0
>>> c_int(2**32).value
0

Another way to see the problem:
>>> c = CDLL(None)
>>> c.printf("%d\n", 2**32)
0
2

This works as designed.  ctypes intentionally does no overflow checking when using the c_int, c_uint, and related integer types.  Instead, only the available bits are used - just as in C.

Closing as invalid (sorry).

An issue remains with the implicit conversion:

On a 64-bit platform (sizeof(long)=64):

>>> c.printf("%d\n",1<<64)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ctypes.ArgumentError: argument 2: <type 'exceptions.OverflowError'>: long int too long to convert

so it does do overflow checking, but

>>> c.printf("%d\n",(1<<64)-1)
-1
3
>>> c.printf("%d\n",(1<<32))
0
2

I must say I do not care too much about the remaining issue.  To be portable between 32-bit and 64-bit platforms you should define .argtypes anyway or explicitely wrap the arguments into ctypes instances, if setting .argtypes is not possible as for printf.