How can I load my homemade 32bit cpp DLL into my canopy 3.5 32bit python?

Question

I am trying to load my DLL (32bit) file containing CPP functions into python. It works on python 3.7 (32bit) but it gives an error when using canopy 3.5 (32bit).

the code I use to load my dll:

import os
import ctypes

os.chdir(r"G:\DLLdirectory")
mydll = ctypes.cdll.LoadLibrary('MyDLL.dll')

If I run it on pyton 3.7 it works, if I run it with canopy 3.5 I get:

Traceback (most recent call last):
    File "DIR/PythonFile.py", line 26, in <module>
        mydll = ctypes.cdll.LoadLibrary('MyDLL.dll')
    File "DIR\Canopy32\edm\envs\User\lib\ctypes\__init__.py", line 425, in LoadLibrary
        return self._dlltype(name)
    File "DIR\Canopy32\edm\envs\User\lib\ctypes\__init__.py", line 347, in __init__
        self._handle = _dlopen(self._name, mode)
OSError: [WinError 126] The specified module could not be found

If you change os.chdir() to sys.path.append() in canopy still the module is not found and in python 3.7 I get this error:

Traceback (most recent call last):
    File "DIR/PythonFile.py", line 26, in <module>
        mydll = ctypes.cdll.LoadLibrary('MyDLL.dll')
    File "DIR\Python\Python37-32\lib\ctypes\__init__.py", line 434, in LoadLibrary
        return self._dlltype(name)
    File "DIR\Python37-32\lib\ctypes\__init__.py", line 356, in __init__
        self._handle = _dlopen(self._name, mode)
OSError: [WinError 193] %1 is not a valid Win32 application

Answer 1

Welcome to StackOverflow!

Not sure whether this is the cause of the error msg that you saw, but FYI the C++ compiler used in building your extension should be the same one used to build the Python that you are using. As you can tell by typing python, Enthought's Python 3.5.2 is built with Visual C++ 2015 (14.0) 1900 See https://stackoverflow.com/a/2676904/1988991

It's likely that you built your DLL with a later compiler. Since it seems to work with Python 3.7, Visual Studio 2017 or 2019 seem likely. See https://www.scivision.dev/python-windows-visual-c-14-required/

Answer 2

It turned out that the DLL was dependent on another DLL and this DLL was found in python automatically. However, in Canopy the second DLL needed to be loaded separately.