test_thread_state() doesn't check that the argument is a function and 
doesn't check function call result and so the exception is catched 
later:

Non callable argument:
   import _testcapi
   _testcapi._test_thread_state(10)
   # no exception raise here
   import gc
   # exception raised too late!
=> TypeError: 'int' object is not callable

Callback error:
   import _testcapi
   def err():
      raise ValueError("xxx")
   _testcapi._test_thread_state(err)
   # no exception raise here
   import gc
   # exception raised too late!
=> ValueError: xxx

So I wrote a patch which fixes that but also raise_exception() which 
have to check that the argument is an exception class.

Python 3.0 has an new function which requires an extra patch: 
exception_print() have to check that the argument is an exception 
instance:

   >>> import _testcapi
   >>> _testcapi.exception_print(10)
   Erreur de segmentation (core dumped)

Your patches are pretty harmless, but this module is just for testing
purposes.

@benjamin.peterson: I know but the module (installed in CPython 
default installation) is for testing purpose only, but invalid uses of 
its method would lead to inconsistent CPython internal state and 
that's bad :-) If you tried to say that such issue is not critical: 
yes, it's just a suggestion to improve CPython ;-)

Unless someone thinks it's somehow release-critical, I'm retargetting
this to 2.7/3.1.

Ok. I'll apply your patches when we get to 2.7. Do ping me if a forget,
though.

@pitrou: This issue is not critical. It's not a bug, it's an 
enhancement since _testcapi :-)

Still, _testcapi is built even for non-debug builds, so it is a
gratuitous way for bad code to crash or internally invalidate a Python
interpreter, so this should be treated like a bugfix.

Fair enough. Fixed in r66000 (trunk) and r66001 (py3k).