using ctypes to use a dll in a python module

using ctypes to use a dll in a python module - Printable Version

+- Python Forum (https://python-forum.io)
+-- Forum: Python Coding (https://python-forum.io/forum-7.html)
+--- Forum: General Coding Help (https://python-forum.io/forum-8.html)
+--- Thread: using ctypes to use a dll in a python module (/thread-41714.html)

using ctypes to use a dll in a python module - dauriac - Mar-05-2024

Hello, working on a windows system and I need to import a dll into a python module. I use ctypes

import ctypes,sys
myLib = ctypes.CDLL("./myDLL.dll")

so far so good but then I want to use a function of the dll. From the .h file
I know there is a function with prototype DWORD ICNC_GetDLLVersion().
I want to call from python, I get

>>> myLib.ICNC_GetDLLVersion()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:/msys64/mingw64/lib/python3.10/ctypes/__init__.py", line 387, in __getattr__
    func = self.__getitem__(name)
  File "C:/msys64/mingw64/lib/python3.10/ctypes/__init__.py", line 392, in __getitem__
    func = self._FuncPtr((name_or_ordinal, self))
AttributeError: function 'ICNC_GetDLLVersion' not found

but I found

>>> myLib[1]
<_FuncPtr object at 0x00000202951206c0>
>>>

and the same for the many functions of the dll.
How can I find the name of the functions as it is in the .h file ?
Thank you

RE: using ctypes to use a dll in a python module - buran - Mar-05-2024

What do you get if you do print(dir(myLib))

RE: using ctypes to use a dll in a python module - dauriac - Mar-06-2024

Thakyou for your answer

Python 3.10.12 (main, Jun 14 2023, 19:14:29)  [GCC 13.1.0 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
pymodbus accessible
>>> import sys,ctypes
>>> myLib = ctypes.CDLL("./ICNC2_VS.dll")
>>> print(dir(myLib))
['_FuncPtr', '__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattr__', '__getattribute__', '
__getitem__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__redu
ce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', '_func_flags_', '_func_restype_', '_handle', '_n
ame']
>>> type(myLib)
<class 'ctypes.CDLL'>

I suspect that the problem comes from the fact that the dll has been compiled in C++, so the name of the function is decorated with the type of arguments an return value.

[solved] using ctypes to use a dll in a python module - dauriac - Mar-06-2024

I recompiled the dll adding extern "C" { } for each function in both the .h and .cpp files, and it solved the problem since the function names are not anymore decorated.