[IronPython] Constructors & inheriting from standard .NET classes

Dino Viehland dinov at microsoft.com
Sat Aug 22 01:41:12 CEST 2009

You need to override and call the base __new__ instead of __init__.  .NET has a simpler construction model than Python does and __new__ is what best corresponds to .NET constructors.

class Derived(Test.Base):
    def __new__(cls, i):
        return Test.Base.__new__(cls, i)

d = Derived()

From: users-bounces at lists.ironpython.com [mailto:users-bounces at lists.ironpython.com] On Behalf Of Zach Crowell
Sent: Friday, August 21, 2009 4:39 PM
To: users at lists.ironpython.com
Subject: [IronPython] Constructors & inheriting from standard .NET classes

I am unable to inherit from .NET classes which do not define a parameterless constructor.  Is this expected behavior? Is there another way to make this inheritance work?

Here's a simple case.

using System;

namespace Test
    public class Base
        public Base(int i)

import clr
import Test

class Derived(Test.Base):
    def __init__(self):

d = Derived()

Traceback (most recent call last):
  File "d:\tmp\class.py", line 9, in d:\tmp\class.py
TypeError: Derived() takes exactly 2 arguments (1 given)

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