Instantiating a python class in C#

Question

I've written a class in python that I want to wrap into a .net assembly via IronPython and instantiate in a C# application. I've migrated the class to IronPython, created a library assembly and referenced it. Now, how do I actually get an instance of that class?

The class looks (partially) like this:

class PokerCard:
    "A card for playing poker, immutable and unique."

    def __init__(self, cardName):

The test stub I wrote in C# is:

using System;

namespace pokerapp
{
    class Program
    {
        static void Main(string[] args)
        {
            var card = new PokerCard(); // I also tried new PokerCard("Ah")
            Console.WriteLine(card.ToString());
            Console.ReadLine();
        }
    }
}

What do I have to do in order to instantiate this class in C#?

Answer 1

IronPython classes are not .NET classes. They are instances of IronPython.Runtime.Types.PythonType which is the Python metaclass. This is because Python classes are dynamic and support addition and removal of methods at runtime, things you cannot do with .NET classes.

To use Python classes in C# you will need to use the ObjectOperations class. This class allows you to operate on python types and instances in the semantics of the language itself. e.g. it uses the magic methods when appropriate, auto-promotes integers to longs etc. You can find out more about ObjectOperations by looking at the source or using reflector.

Here is an example. Calculator.py contains a simple class:

class Calculator(object):
    def add(self, a, b):
        return a + b

You can use it from your pre .NET 4.0 C# code like this:

ScriptEngine engine = Python.CreateEngine();
ScriptSource source = engine.CreateScriptSourceFromFile("Calculator.py");
ScriptScope scope = engine.CreateScope();

ObjectOperations op = engine.Operations;

source.Execute(scope); // class object created
object klaz = scope.GetVariable("Calculator"); // get the class object
object instance = op.Call(klaz); // create the instance
object method = op.GetMember(instance, "add"); // get a method
int result = (int)op.Call(method, 4, 5); // call method and get result (9)

You will need to reference the assemblies IronPython.dll, Microsoft.Scripting and Microsoft.Scripting.Core.

C# 4 made this much easier with the new dynamic type.

ScriptEngine engine = Python.CreateEngine();
ScriptSource source = engine.CreateScriptSourceFromFile("Calculator.py");
ScriptScope scope = engine.CreateScope();
source.Execute(scope);

dynamic Calculator = scope.GetVariable("Calculator");
dynamic calc = Calculator();
int result = calc.add(4, 5);

If you are using Visual Studio 2010 or later with NuGet support simply execute this to download and reference the appropriate libraries.

Install-Package IronPython