[Python-Dev] Let's update CObject API so it is safe and regular!

Thu Apr 2 01:26:15 CEST 2009

Jim Fulton wrote:
> The only type-safety mechanism for a CObject is it's identity. If you 
> want to make sure you're using the foomodule api, make sure the 
> address of the CObject is the same as the address of the api object 
> exported by the module.
That doesn't help. Here's a program that crashes the interpreter, 
something I shouldn't be able to do from pure Python:
 import _socket
 import cStringIO
 cStringIO.cStringIO_CAPI = _socket.CAPI
 import cPickle
 s = cPickle.dumps([1, 2, 3])
How can cPickle determine that cStringIO.cStringIO_CAPI is legitimate?
> That would break backward compatibility. Are you proposing this for 
> Python 3?

I'm proposing this for Python 3.1. My understanding is that breaking 
backwards compatibility is still on the table, which is why I wrote the 
patch the way I did. If we have to preserve the existing API, I still 
think we should add new APIs and deprecate the old ones.
It's worth noting that there's been demand for this for a long time. 
Check out this comment from Include/datetime.h:
 #define PyDateTime_IMPORT \
 PyDateTimeAPI = (PyDateTime_CAPI*)
 PyCObject_Import("datetime", \

 "datetime_CAPI")
 /* This macro would be used if PyCObject_ImportEx() was created.
 #define PyDateTime_IMPORT \
 PyDateTimeAPI = (PyDateTime_CAPI*)
 PyCObject_ImportEx("datetime", \

 "datetime_CAPI", \

 DATETIME_API_MAGIC)
 */
That was checked in by Tim Peters on 2004年06月20日, r36214. (At least, in 
the py3k/trunk branch; I'd hope it would be the same revision number in 
other branches.)
/larry/
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