Python inheritance: TypeError: object.__init__() takes no parameters

Question

I get this error:

TypeError: object.__init__() takes no parameters 

when running my code, I don't really see what I'm doing wrong here though:

class IRCReplyModule(object):

    activated=True
    moduleHandlerResultList=None
    moduleHandlerCommandlist=None
    modulename=""

    def __init__(self,modulename):
        self.modulename = modulename


class SimpleHelloWorld(IRCReplyModule):

     def __init__(self):
            super(IRCReplyModule,self).__init__('hello world')

Solution 1

You are calling the wrong class name in your super() call:

class SimpleHelloWorld(IRCReplyModule):

     def __init__(self):
            #super(IRCReplyModule,self).__init__('hello world')
            super(SimpleHelloWorld,self).__init__('hello world')

Essentially what you are resolving to is the __init__ of the object base class which takes no params.

Its a bit redundant, I know, to have to specify the class that you are already inside of, which is why in python3 you can just do: super().__init__()

Solution 2

This has bitten me twice recently (I know I should have learned from my mistake the first time) and the accepted answer hasn't helped me either time so while it is fresh in my mind I thought I would submit my own answer just in case anybody else is running into this (or I need this again in future).

In my case the issue was that I was passing a kwarg into the initialisation of the subclass but in the superclass that keyword arg was then being passed though into the super() call.

I always think these types of things are best with an example:

class Foo(object):
  def __init__(self, required_param_1, *args, **kwargs):
    super(Foo, self).__init__(*args, **kwargs)
    self.required_param = required_param_1
    self.some_named_optional_param = kwargs.pop('named_optional_param', None)

  def some_other_method(self):
    raise NotImplementedException

class Bar(Foo):
  def some_other_method(self):
    print('Do some magic')


Bar(42) # no error
Bar(42, named_optional_param={'xyz': 123}) # raises TypeError: object.__init__() takes no parameters

So to resolve this I just need to alter the order that I do things in the Foo.__init__ method; e.g.:

class Foo(object):
  def __init__(self, required_param_1, *args, **kwargs):
    self.some_named_optional_param = kwargs.pop('named_optional_param', None)
    # call super only AFTER poping the kwargs
    super(Foo, self).__init__(*args, **kwargs)
    self.required_param = required_param_1