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[3.6] bpo-30470: Deprecate invalid ctypes call protection on Windows.… #1833

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Mariatta merged 1 commit into from
May 27, 2017
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[3.6] bpo-30470: Deprecate invalid ctypes call protection on Windows.… #1833

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20 changes: 6 additions & 14 deletions Doc/library/ctypes.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -161,22 +161,14 @@ as the NULL pointer)::
0x1d000000
>>>

:mod:`ctypes` tries to protect you from calling functions with the wrong number
of arguments or the wrong calling convention. Unfortunately this only works on
Windows. It does this by examining the stack after the function returns, so
although an error is raised the function *has* been called::
.. note::

>>> windll.kernel32.GetModuleHandleA() # doctest: +WINDOWS
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: Procedure probably called with not enough arguments (4 bytes missing)
>>> windll.kernel32.GetModuleHandleA(0, 0) # doctest: +WINDOWS
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: Procedure probably called with too many arguments (4 bytes in excess)
>>>
:mod:`ctypes` may raise a :exc:`ValueError` after calling the function, if
it detects that an invalid number of arguments were passed. This behavior
should not be relied upon. It is deprecated in 3.6.2, and will be removed
in 3.7.

The same exception is raised when you call an ``stdcall`` function with the
:exc:`ValueError` is raised when you call an ``stdcall`` function with the
``cdecl`` calling convention, or vice versa::

>>> cdll.kernel32.GetModuleHandleA(None) # doctest: +WINDOWS
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