Can't import dll module in Python
I've been stressin for a few days trying to compile a modified version of libuvc on windows and now that I've finally done it, I can't seem to load it on Python. This lib that I've already compiled and successfully imported using the same version of Python on Linux machines, doesn't like w10 at all.
System
- win 10 64 bit
- python 3.8 64 bit
- libusb 1.022
- libuvc.dll compiled with MinGW64
Problem
When trying the
import ctypes
import ctypes.util
name = ctypes.util.find_library('libuvc')
lib = ctypes.cdll.LoadLibrary(name)
I get the following error:
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!
The issue is that the file exists since it was found by util.find_library, but python doesn't think it is where it is, or maybe the output is just the default. What am I missing here? What could be failing to be unable to not just load the module, but find it? I'm sorry I don't have more output than this.
P.S: I've tried reformatting the string in different ways, but the message doesn't change.
Answer
Starting with Python 3.8, the .dll search mechanism has changed.
According to [Python.Docs]: os.add_dll_directory(path) (emphasis is mine):
Add a path to the DLL search path.
This search path is used when resolving dependencies for imported extension modules (the module itself is resolved through sys.path), and also by ctypes.
So, you could do:
os.add_dll_directory("${path_to_working_dlls_directoy}")
You can check [SO]: PyWin32 and Python 3.8.0 (@CristiFati's answer) (which although it seems very different, has the same cause), for more details.