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".

bpo-39393 improved the error message to mention "(or one of its dependencies)". That's the best we can reasonably do. A developer can monitor "loader snaps" messages in a debugger in order to discover the missing DLL and the directories where the loader looked for it.