Precautions and error handling when calling .NET DLL from python using pythonnet

pythonnet --What is Python.NET?

A library that allows you to call DLLs for .NET from Python. It is MIT licensed and anyone can use it free of charge. https://github.com/pythonnet/pythonnet

How to use

This article was very helpful for how to use it. How to call .NET from Python and vice versa

Here is a brief introduction.

Installation method

pip install pythonnet

Example of use

If you want to use ABCLib.dll in the same directory as test.py. If it is in another directory, add the path as appropriate. clr.AddReference ('./DEF/ABCLib') etc.

test.py

import clr

clr.AddReference('ABCLib')
from ABCTools import ABCLib

abc = ABCLib()

clr seems to be an abbreviation for Common Language Runtime.

Precautions and what to do when an error occurs

Here are some points I stumbled upon when using pythonnet and how to target them.

Do not write .dll

** Error: System.IO.FileNotFoundException: Unable to find assembly'ABCLib.dll'. ** I get this error if I write the extension'.dll' when doing clr.AddReference. Let's delete the'.dll'.

#Example of error
clr.AddReference('ABCLib.dll')

#Example where no error occurs
clr.AddReference('ABCLib')

Allow security

** Error: System.IO.FileNotFoundException: Unable to find assembly'ABCLib'. ** If the dll is obtained from the outside, access to the file may be blocked. Try setting to allow access. Right-click on the dll file → Properties → General → Check "Allow" at the bottom → OK

Match 64bit / 32bit with DLL and Python

** Error: System.IO.FileNotFoundException: Could not load file or assembly'ABCLib, Version = ~~~~~~~~, Culture = neutral, PublicKeyToken = null', or one of its dependencies. The specified file could not be found. ** **

It could not be read unless the DLL and Python bits match.

--How to check Python bits

python

import sys
print(sys.version)

output

3.7.6 (tags/v3.7.6:43364a7ae0, Dec 19 2019, 00:42:30) [MSC v.1916 64 bit (AMD64)]

--How to check the bit of DLL I referred to this article. How to check if EXE or DLL is 32bit or 64bit -Qiita