In Python, can you call an instance method of class A, but pass in an instance of class B?

Question

In the interest of reusing some existing code that was defined as an instance method of a different class, I was tying to do something like the following:

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Answer 1

This is an old question, but Python has evolved and looks like it's worth pointing it out:

with Python 3 there's no more , since an unbound method is simply a !

Which probably means the code in the original question should not be considered /that/ off. Python has always been about duck typing in any case, hasn't it?!

Refs:

• Guido proposing to remove unbound methods from python
• What's new for Python 3 release
• Get defining class of unbound method object in Python 3

Alternative solution in Py2

Note that there's also an alternative solution to the "explorative" question (see Python: Bind an Unbound Method?):

In [6]: a = A.a.im_func.__get__(B(), B)

In [7]: a
Out[7]: >

In [8]: a(2)
2

Ref:

Some ipython code samples

python 2

In [1]: class A():
    def a(self, a=0):
        print a
   ...:

In [2]: A.a
Out[2]: 

In [3]: A.a.im_func
Out[3]: 

In [4]: A.a(B())
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
 in ()
----> 1 A.a(B())

TypeError: unbound method a() must be called with A instance as first argument (got B instance instead)

python 3

In [2]: class A():
    def a(self, a=0):
        print(a)
   ...:

In [3]: def a():
   ...:     pass
   ...:

In [4]: class B():
   ...:     pass

In [5]: A.a(B())
0

In [6]: A.a
Out[6]: