Multiple inheritance, super() and changing signature
Nagy László Zsolt
gandalf at shopzeus.com
Fri Jun 3 10:06:12 EDT 2016
>> That's overly strict. As Raymond shows, it is easy to deal with
>> changing method signatures in *cooperative* classes.
> 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 = param1
self.param2 = param2
super().__init__(**kwds)
class B:
def __init__(self, param1, param3, **kwds):
self.param1 = param1
self.param3 = param3
super().__init__(**kwds)
class X(A,B):
def __init__(self, param1, param2, param3, **kwds):
print("param1=",param1,"param2=",param2,"param3=",param3)
super().__init__(param1=param1,param2=param2,param3=param3,**kwds)
print(X.__mro__)
x = X(1,2,3)
Result:
(<class '__main__.X'>, <class '__main__.A'>, <class '__main__.B'>,
<class 'object'>)
param1= 1 param2= 2 param3= 3
Traceback (most recent call last):
File "test.py", line 20, in <module>
x = X(1,2,3)
File "test.py", line 17, in __init__
super().__init__(param1=param1,param2=param2,param3=param3,**kwds)
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 = kwds['param1']
self.param2 = kwds['param2']
super().__init__(**kwds)
class B(Root):
def __init__(self, **kwds):
self.param1 = kwds['param1']
self.param3 = kwds['param3']
super().__init__(**kwds)
class X(A,B):
def __init__(self, param1, param2, param3, **kwds):
print("param1=",param1,"param2=",param2,"param3=",param3)
super().__init__(param1=param1,param2=param2,param3=param3,**kwds)
X(1,2,3)
But then self documentation and code completion becomes very problematic:
http://i.imgur.com/wzlh8uy.png
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