[New-bugs-announce] [issue40610] ctypes on Windows: error message on DLL load failure is misleading

[Jack Jansen]

New submission from Jack Jansen <Jack.Jansen at cwi.nl>:

On Windows, when ctypes fails to load a DLL, the error message is misleading. If a dependency of the DLL cannot be found if appears as if the DLL itself cannot be found.

This issue has always existed on Windows (and I know it is due to what the OS provides by default as its error message) but it is exacerbated by the DLL loading rules in Python 3.8 (the `os.add_dll_directory()` changes), because now importing a DLL into Python will follow different rules than those followed by, for example, command line utilities shipped with the DLL you are loading follow.

An ideal fix would be a message of the form "xxx.dll failed to load because its dependency yyy.dll is not on the current Python DLL search path, see zzzz for details". But I am not well-versed enough in Windows APIs to know whether that is even possible.

A fix that is minimal and at least not misleading would be a message "xxx.dll (or one of its dependencies) failed to load. See zzzz for details".

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components: ctypes
messages: 368748
nosy: jackjansen
priority: normal
severity: normal
status: open
title: ctypes on Windows: error message on DLL load failure is misleading
type: enhancement
versions: Python 3.8

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue40610>
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