How to pass python callback to c# function call

Question

I am trying to use C# classes from python, using python.net on mono / ubuntu.

So far I managed to do a simple function call with one argument work. What I am now trying to do is pass a python callback to the C# function call.

I tried the following variations below, none worked. Can someone show how to make that work?

// C# - testlib.cs
class MC {
    public double method1(int n) {
        Console.WriteLine("Executing method1" );
        /* .. */
    }

    public double method2(Delegate f) {
        Console.WriteLine("Executing method2" );
        /* ... do f() at some point ... */
        /* also tried f.DynamicInvoke() */
        Console.WriteLine("Done executing method2" );
    }
}

Python script

import testlib, System
mc = testlib.MC()
mc.method1(10) # that works

def f():
    print "Executing f"

mc.method2(f)  
# does not know of method2 with that signature, fair enough...

# is this the right way to turn it into a callback?
f2 = System.AssemblyLoad(f) 
# no error message, but f does not seem to be invoked
mc.method2(f2)              

Answer 1

Try to pass Action or Func instead of just raw function:

I used IronPython here (because right now I don't have mono installed on any of my machines but according of Python.NET documentation I think it should work Actually your code is almost ok but you need to import Action or Func delegate depends on what you need.

python code:

import clr
from types import *
from System import Action
clr.AddReferenceToFileAndPath(r"YourPath\TestLib.dll")
import TestLib
print("Hello")
mc = TestLib.MC()
print(mc.method1(10))

def f(fakeparam):
    print "exec f" 

mc.method2(Action[int](f))

This is a console output:

Hello
Executing method1
42.0
Executing method2
exec f
Done executing method2

C# code:

using System;


namespace TestLib
{
    public class MC
    {
        public double method1(int n)
        {
            Console.WriteLine("Executing method1");
            return 42.0;
            /* .. */
        }

        public double method2(Delegate f)
        {
            Console.WriteLine("Executing method2");
            object[] paramToPass = new object[1];
            paramToPass[0] = new int();
            f.DynamicInvoke(paramToPass);
            Console.WriteLine("Done executing method2");
            return 24.0;

        }
    }
}

I read docs for Python.net Using Generics again and also found this Python.NET Naming and resolution of generic types look like you need to specify parameter type explicitly

quote from there:

a (reflected) generic type definition (if there exists a generic type definition with the given base name, and no non-generic type with that name). This generic type definition can be bound into a closed generic type using the [] syntax. Trying to instantiate a generic type def using () raises a TypeError.