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ctypes.util.find_library does not respect os.add_dll_directory #111104
Description
Activity
Did you ever find a solution to this?
Using Python 3.12.6 and Windows 11 64-bit, I am also struggling with
ctypes.util.find_library()not finding DLLs in directories added byos.add_dll_directory(), but will locate them if the full path to the DLL is provided tofind_library(). Unfortunately this breaks an imported module that usesfind_library()with the DLL name to locate a DLL.Test folder structure:
tester.py:
import os from pathlib import Path from ctypes.util import find_library # Add the directory this script is in (also contains vxlapi64.dll) add_obj = os.add_dll_directory(os.path.dirname(__file__)) # Check for library using DLL name if find_library("vxlapi64"): print("vxlapi64.dll from add_dll_directory found") else: print("vxlapi64.dll from add_dll_directory NOT FOUND") # Check for library using DLL path if find_library(os.path.dirname(__file__) + "/vxlapi64"): print("vxlapi64.dll abs path found") else: print("vxlapi64.dll abs path NOT FOUND")
Output of
python tester.py:vxlapi64.dll from add_dll_directory NOT FOUND vxlapi64.dll abs path foundI'm proposing to soft-deprecate
ctypes.util.find_library: https://discuss.python.org/t/106232Reacted by mara004It is now soft-deprecated. It cannot be made to work correctly and consistently on all platforms, and any change runs a chance to break whatever workarounds people already have in place.
I'm prioritizing stability over new features, and encourage solving this outside ctypes itself.Reacted by David Van Arnem
Bug report
Bug description:
os.add_dll_directory's documentation states that "This search path is used when resolving dependencies for imported extension modules (the module itself is resolved through sys.path), and also by ctypes.", yet paths added there do not affect ctypes.util.find_library (one can easily verify that the implementation of the latter simply walks PATH:
cpython/Lib/ctypes/util.py
Lines 55 to 68 in b4c215e
I do realize that find_library's doc does state "The purpose of the find_library() function is to locate a library in a way similar to what the compiler or runtime loader does (on platforms with several versions of a shared library the most recent should be loaded), while the ctypes library loaders act like when a program is run, and call the runtime loader directly." which might justify the difference in behavior; still, it would be nice if ctypes provided a function (or changed find_library) to return the path of the library that would be loaded while respecting add_dll_directory (right now a workaround would be to call GetModuleFileNameEx ourselves on the handle returned by WinDLL).
CPython versions tested on:
3.12
Operating systems tested on:
Windows