Why Can\'t Python Find My libuvc.dll on Windows?

Troubleshooting Unable to Import DLL Module in Python

Problem Statement:

In an attempt to import a modified version of libuvc on Windows using Python 3.8, the following error is encountered:

Could not find module 'C:\Program Files (x86)\libuvc\lib\libuvc.dll'.
Try using the full path with constructor syntax.
Error: could not find libuvc!

Analysis:

The error message suggests that Python is unable to locate the libuvc.dll file despite it being found by util.find_library. This indicates a discrepancy in the search method used by ctypes.DLL.LoadLibrary.

Solution:

By bypassing the default search mode, the issue can be resolved by specifying the winmode=0 parameter in the LoadLibrary constructor. This forces the search mode to include the full path to the DLL, allowing Python to locate and load it successfully.

Detailed Explanation:

• The default search mode (nt._LOAD_LIBRARY_SEARCH_DEFAULT_DIRS) does not respond to changes in search paths defined by the environment.
• By setting winmode=0 (nt._LOAD_WITH_ALTERED_SEARCH_PATH), the search mode is set to explicitly include the full path to the DLL.
• Prior to Python 3.8, the winmode parameter did not exist, and the default value of mode corresponded to zero, which worked on all platforms.

Additional Notes:

• To ensure the DLL is properly located, verify that it is present at the path specified by util.find_library.
• For more detailed information on the ctypes.DLL behavior, refer to the Microsoft documentation: https://learn.microsoft.com/en-us/windows/win32/api/libloaderapi/nf-libloaderapi-loadlibraryexa

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