adding dynamically a new parent class to an existing object

Asked Feb 21 '20 at 20:36

Active Feb 21 '20 at 20:36

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How can one add dynamically a new parent class in python to an existing object?

class A:
    def doA(self): print('A::doA')

class C(A): pass

c = C()

# class 'B' is created after object 'c'
class B:
    def doB(self): print('B::doB')

# XXX: python magic here, which adds dynamically 'B' to the list of parent classes of 'C'
#      as if 'C' was created like this "class C(A,B): pass"

c.doB() # works

asked Feb 21 '20 at 20:36

S.V

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Does this answer your question? [Dynamic inheritance in Python](https://stackoverflow.com/questions/21060073/dynamic-inheritance-in-python) – cwalvoort Feb 21 '20 at 20:40
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There no good way to do this, and this seems like a fundamental design problem – juanpa.arrivillaga Feb 21 '20 at 20:40
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@cwalvoort That adds a parent dynamically to a class, not to an instance. – Barmar Feb 21 '20 at 20:42
@Barmar, ah, read it wrong. My mistake. – cwalvoort Feb 21 '20 at 20:45
1

This _almost_ gets you there but you'd have to create `c` after modifying the class: https://stackoverflow.com/questions/9539052/how-to-dynamically-change-base-class-of-instances-at-runtime – Michoel Feb 21 '20 at 21:04
@Michoel Thank you! It works! The missing "python magic" is `C.__bases__ = (A, B)` – S.V Feb 21 '20 at 21:11

adding dynamically a new parent class to an existing object

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