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Newsgroups: comp.lang.python
Subject: Re: Multiple inheritance, super() and changing signature
Date: Fri, 3 Jun 2016 16:06:12 +0200
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>> That's overly strict. As Raymond shows, it is easy to deal with
>> changing method signatures in *cooperative* classes.=20
> I must watch that for sure.

All right, I have read this:

https://rhettinger.wordpress.com/2011/05/26/super-considered-super/

There is still something I don't get: how to create cooperative classes
when some base classes share some of the parameters?

Here is an example modified from Raymond's post:

class A:
    def __init__(self, param1, param2, **kwds):
        self.param1 =3D param1
        self.param2 =3D param2
        super().__init__(**kwds)

class B:
    def __init__(self, param1, param3, **kwds):
        self.param1 =3D param1
        self.param3 =3D param3
        super().__init__(**kwds)


class X(A,B):
    def __init__(self, param1, param2, param3, **kwds):
        print("param1=3D",param1,"param2=3D",param2,"param3=3D",param3)
        super().__init__(param1=3Dparam1,param2=3Dparam2,param3=3Dparam3,=
**kwds)

print(X.__mro__)
x =3D X(1,2,3)


Result:

(<class '__main__.X'>, <class '__main__.A'>, <class '__main__.B'>,
<class 'object'>)
param1=3D 1 param2=3D 2 param3=3D 3
Traceback (most recent call last):
  File "test.py", line 20, in <module>
    x =3D X(1,2,3)
  File "test.py", line 17, in __init__
    super().__init__(param1=3Dparam1,param2=3Dparam2,param3=3Dparam3,**kw=
ds)
  File "test.py", line 5, in __init__
    super().__init__(**kwds)
TypeError: __init__() missing 1 required positional argument: 'param1'

I could only find this as a solution:

class Root:
    def __init__(self, **kwds):
        pass

class A(Root):
    def __init__(self, **kwds):
        self.param1 =3D kwds['param1']
        self.param2 =3D kwds['param2']
        super().__init__(**kwds)

class B(Root):
    def __init__(self, **kwds):
        self.param1 =3D kwds['param1']
        self.param3 =3D kwds['param3']
        super().__init__(**kwds)


class X(A,B):
    def __init__(self, param1, param2, param3, **kwds):
        print("param1=3D",param1,"param2=3D",param2,"param3=3D",param3)
        super().__init__(param1=3Dparam1,param2=3Dparam2,param3=3Dparam3,=
**kwds)

X(1,2,3)

But then self documentation and code completion becomes very problematic:=


http://i.imgur.com/wzlh8uy.png