From b6f2fc90409e291822166d74ce7402e0ef4dba91 Mon Sep 17 00:00:00 2001 From: Philippe Ombredanne Date: Thu, 22 Oct 2020 17:39:18 +0200 Subject: [PATCH] bpo-25655: Improve Win DLL loading failures doc (GH-22372) Add documentation to help diagnose CDLL dependent DLL loading errors on windows for OSError with message: "[WinError 126] The specified module could not be found" This error is otherwise difficult to diagnose. --- Doc/library/ctypes.rst | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/Doc/library/ctypes.rst b/Doc/library/ctypes.rst index c172d537763..bf32d3e549b 100644 --- a/Doc/library/ctypes.rst +++ b/Doc/library/ctypes.rst @@ -1326,6 +1326,21 @@ way is to instantiate one of the following classes: libraries use the standard C calling convention, and are assumed to return :c:type:`int`. + On Windows creating a :class:`CDLL` instance may fail even if the DLL name + exists. When a dependent DLL of the loaded DLL is not found, a + :exc:`OSError` error is raised with the message *"[WinError 126] The + specified module could not be found".* This error message does not contain + the name of the missing DLL because the Windows API does not return this + information making this error hard to diagnose. To resolve this error and + determine which DLL is not found, you need to find the list of dependent + DLLs and determine which one is not found using Windows debugging and + tracing tools. + +.. seealso:: + + `Microsoft DUMPBIN tool `_ + -- A tool to find DLL dependents. + .. class:: OleDLL(name, mode=DEFAULT_MODE, handle=None, use_errno=False, use_last_error=False, winmode=0)