python3 pythonnet generic delegates

Question

I have 64bit CPython 3.4 installation on windows7. I use the pythonnet package (2.0.0.dev1). I want to instantiate the action delegate, but it gives me an error.

def display(num):
     print("num=", num)

import clr
clr.AddReference("System")
import System

paction=System.Action[System.Int32](display)

I get this error:

TypeError Traceback (most recent call last) in () ----> 1 paction=System.Action[System.Int32](display) TypeError: unsubscriptable object

I guess this is the way one shall specify generics.

I have checked the docu and this post, and still do not see the problem. I also palyed around a bit with the Overload method, but did not help either:

paction=System.Action.Overloads[System.Int32](display)

TypeError Traceback (most recent call last) in () ----> 1 paction=System.Action.Overloads[System.Int32](display) TypeError: No match found for constructor signature

Answer 1

The problem is that System.Action (without arguments and thus not a generic) is shadowing System.Action<T> while System.Func maps directly to System.Func<T>. I guess this is because System.Func will always have a generic parameter and there seems to be an overload implementation in place for generics.

The generic's name in Python.NET is Action`1 (in general: Action`N with N being the number of generic arguments). You can get the wrapper object by using getattr on the module:

Action = getattr(System, "Action`1")
action = Action[Int32](display)

Answer 2

I'm also facing this problem. I created a work around to use Actions in Python.Net

Create a .net class library project with the following code:

using System;

namespace PythonHelper
{
    public class Generics
    {

        public static Action<T1, T2> GetAction<T1, T2>(Func<T1, T2, object> method)
        {
            return (a, b) => method(a,b);
        }

    }
}

Compile this to a dll file and include it in your Python.net project (clr.AddReference('PythonHelper'))

Now in your Python.net project you can create generics with following code:

import clr
clr.AddReference('PythonHelper')
import System
from System import DateTime, Func
from PythonHelper import Generics

def myCallback(a,b):
    print a, b

func = Func[DateTime, DateTime, System.Object](myCallback)
action = Generics.GetAction[DateTime, DateTime](func)

If you need to create an action with more or less params, you have to add another GetAction method yourself.