Add more checks to testcapi

[vstinner]

BPO	3643
Nosy	@birkenfeld, @pitrou, @vstinner, @devdanzin, @benjaminp
Files	testcapi_py26.patch: Fix _test_thread_state() and raise_exception() and _testcapi module testcapi_py30.patch: Fix exception_print() of _testcapi module

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/benjaminp'
closed_at = <Date 2008-08-23.20:33:11.508>
created_at = <Date 2008-08-22.01:41:22.063>
labels = ['type-feature', 'library']
title = 'Add more checks to testcapi'
updated_at = <Date 2008-08-23.20:33:11.393>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2008-08-23.20:33:11.393>
actor = 'benjamin.peterson'
assignee = 'benjamin.peterson'
closed = True
closed_date = <Date 2008-08-23.20:33:11.508>
closer = 'benjamin.peterson'
components = ['Library (Lib)']
creation = <Date 2008-08-22.01:41:22.063>
creator = 'vstinner'
dependencies = []
files = ['11204', '11205']
hgrepos = []
issue_num = 3643
keywords = ['patch']
message_count = 9.0
messages = ['71714', '71715', '71716', '71730', '71735', '71770', '71808', '71810', '71814']
nosy_count = 5.0
nosy_names = ['georg.brandl', 'pitrou', 'vstinner', 'ajaksu2', 'benjamin.peterson']
pr_nums = []
priority = 'high'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue3643'
versions = ['Python 2.6', 'Python 3.0']

[vstinner]

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.

[vstinner]

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)

[benjaminp]

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

[vstinner]

@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 ;-)

[pitrou]

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

[benjaminp]

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

[vstinner]

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

[birkenfeld]

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.

[benjaminp]

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