using unbound methods in another python class

Question

I have an unbound method as <unbound method foo.ops>, i would like to use the same method with another class. take an example

class foo2(object):
  pass

foo2.ops = foo.ops

however

obj = foo2()
obj.ops()

raises TypeError: unbound method ops() must be called with foo instance as first argument (got nothing instead)

Take the hint. Don't do this. You have inheritance. Use inheritance for this. Not magic. — S.Lott, Apr 18 '11 at 10:04

9000 · Accepted Answer · 2013-09-23T06:04:16.727

11

If you want to add the same method to several unrelated classes (e.g. doing AOP), don't copy an unbound method from one of them. Instead, define a plain function and assign it as a method to every class.

Usually a better way to do it is a mixin (using plain inheritance) or a metaclass (class decorator syntax is neat).

If you're hell-bound to steal a method from a class (e.g. one you don't control), you can extract it from the 'unbound method' wrapper: foo2.ops.im_func; it's a plain function and you can assign it as a method to another class.

edited Sep 23 '13 at 06:04

answered Apr 18 '11 at 11:32

9000

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Could you provide an example using a mixin or a metaclass? – Tony Baguette Jul 01 '14 at 20:12

Andrey Sboev · Answer 2 · 2011-04-18T10:27:07.587

0

If you want to implement 'class methods', you should call it accordingly, whithout object instance

class foo:
    @staticmethod
    def ops(name):
        print "Hi there",name

foo.ops("Peter")

class foo2:
    pass

foo2.ops = staticmethod(foo.ops)

foo2.ops('aa')

(copy-pasted from http://code.activestate.com/recipes/52304-static-methods-aka-class-methods-in-python/)

if you want instance method, use inheritance

edited Apr 18 '11 at 10:27

answered Apr 18 '11 at 10:09

Andrey Sboev

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The example is more than 8 years old, you can use @staticmethod now. – Sebastian Blask Apr 18 '11 at 10:15
but it doesn't work if we want to copy method to another class, does it? – Andrey Sboev Apr 18 '11 at 10:18
@staticmethod does the same as Callable, but the original question needs something like: foo2.ops = staticmethod(foo.ops) S.Lott is right though, it shouldn't be used... – Sebastian Blask Apr 18 '11 at 10:25

using unbound methods in another python class

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