CODEWITHSUNDEEP
pythonpython-2.7
Stephen
Stephen

Reputation: 2863

Python 2 dynamic multiple inheritance

In python 3 I can use list expansion to dynamically inherit from multiple superclasses:

class Super1(object):
    x = 1

class Super2(object):
    y = 1

classes = [Super1, Super2]

class B(*classes):
    pass

This lets me allow for runtime decisions about which mixin classes to add to the list of superclasses.

Unfortunately, the * expansion of the superclass list is a syntax error in python2. Is there a generally accepted way of choosing the list of superclasses at runtime

Upvotes: 2

Views: 46

Answers (2)

Stephen
Stephen

Reputation: 2863

The answer provided by @blhsing is correct, but I actually wanted something that was 2/3 compatible. I took the cue of using type directly and did something more like this:

class Super1(object):
    x = 1

class Super2(object):
    y = 1

classes = [Super1, Super2]

B = type('B', tuple(classes), {})

Which works equally well in 2/3

Upvotes: 2

blhsing
blhsing

Reputation: 107134

You can use a metaclass to populate B's base classes instead:

classes = Super1, Super2

class B:
    __metaclass__ = lambda name, _, attrs: type(name, classes, attrs)

print(B.__bases__)

This outputs:

(<class '__main__.Super1'>, <class '__main__.Super2'>)

Upvotes: 1

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