Python: Inherit the superclass __init__

Question

I have a base class with a lot of __init__ arguments:

class BaseClass(object):
    def __init__(self, a, b, c, d, e, f, ...):
        self._a=a+         


        

Answer 1

Unless you are doing something useful in the subclass __init__() methods, you don't have to override it.

def BaseClass(object):
    def __init__(self, a, b, c, d, e, f, ...):
        self._a=a+b
        self._b=b if b else a
        ...

def A(BaseClass):
    def some_other_method(self):
        pass

def B(BaseClass):
    pass

Answer 2

Perhaps a clearer implementation for your case is using **kwargs combined with new added arguments in your derived class as in:

class Parent:
    def __init__(self, a, b, c):
        self.a = a
        self.b = b
        self.c = c


class Child(Parent):
    def __init__(self, d, **kwargs):
        super(Child, self).__init__(**kwargs)
        self.d = d

By this method you avoid the code duplication but preserve the implicit addition of arguments in your derived class.

Answer 3

If the derived classes don't implement anything beyond what the base class __init__() already does, just omit the derived classes __init__() methods - the base class __init__() is then called automatically.

If, OTOH, your derived classes add some extra work in their __init__(), and you don't want them to explicitly call their base class __init__(), you can do this:

class BaseClass(object):
    def __new__(cls, a, b, c, d, e, f, ...):
        new = object.__new__(cls)
        new._a=a+b
        new._b=b if b else a
        ...
        return new

class A(BaseClass):
    ''' no __init__() at all here '''

class B(BaseClass):
    def __init__(self, a, b, c, d, e, f, ...):
        ''' do stuff with init params specific to B objects '''

Since __new__() is always called automatically, no further work is required in the derived classes.

Answer 4

Adding a Pythonic implementation. Assuming you want all attributes passed in, you can use the code below. (Can also keep/remove specific kwargs keys if you want a subset).

def A(BaseClass):
    def __init__(self, *args, **kwargs):
        for key, value in kwargs.items():
            setattr(self, key, value)

base = BaseClass(...)
new = A( **base.__dict__ )

Answer 5

super(SubClass, self).__init__(...)

Consider using *args and **kw if it helps solving your variable nightmare.

Answer 6

In 2.6 and lower version to inherit init from base class, there is no super function, You can inherit below way:

class NewClass():
     def __init__():
         BaseClass.__init__(self, *args)