Why Can\'t I Import My DLL Module in Python on Windows 10?

Cannot Import DLL Module in Python: An In-Depth Guide

Despite successful compilation on Linux machines, importing a modified version of libuvc into Python on Windows 10 presents a challenge. This article will delve into the problem and provide a solution.

System Details:

• Windows 10 64-bit
• Python 3.8 64-bit
• Libusb 1.022
• Libuvc.dll compiled with MinGW64

Problem Description:

When attempting to import the DLL using the following code:

<code class="python">import ctypes
import ctypes.util
name = ctypes.util.find_library('libuvc')
lib = ctypes.cdll.LoadLibrary(name)</code>

An error appears:

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:

• Path Finding Issue: ctypes.util.find_library() correctly identifies the DLL's location.
• Incorrect Loading Mode: The problem stems from an incorrect loading mode used by ctypes.cdll.LoadLibrary().

Solution:

1. Adjust Loading Mode:

By explicitly setting winmode=0 in the ctypes.cdll.LoadLibrary() constructor, the DLL's loading mode is set to search in specific default directories. This modification bypasses the default search mechanism, which may not recognize changes to system paths.

<code class="python">lib = ctypes.cdll.LoadLibrary(name, winmode=0)</code>

2. Historical Context:

In Python versions prior to 3.8, the winmode parameter did not exist. The default mode value of ctypes.DEFAULT_MODE coincided with winmode=0, resolving this issue unintentionally. However, in Python 3.8 and later, winmode must be explicitly specified.

Conclusion:

Adjusting the loading mode using winmode=0 resolves the issue of importing the DLL module in Python on Windows 10. This solution addresses an incompatibility introduced in Python 3.8, allowing for successful DLL integration.

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