Python multiple inheritance property

Question

In the following code C is inherited from A and B so when c.get() is get which classes get method is called can anyone explain this.....

class A:
  def get(self):
    print "In A get"

class B:
  def get(self):
    print "In B get"

class C(A,B):
  def __init__(self):
    print "In c init"

c=C()
c.get()

Maybe this will help: http://stackoverflow.com/questions/3810410/python-multiple-inheritance-from-different-paths-with-same-method-name — Bartosz Grzybowski, Mar 14 '12 at 16:45
If you actually tried to run this, you would find that it doesn't work, because none of your methods take a parameter. — Marcin, Mar 14 '12 at 16:47
@Marcin: Shouldn't make a difference here. Also, it seems to be Python 2 (although it's not quite valid Python2, either). — Niklas B., Mar 14 '12 at 16:47
@NiklasB. Isn't method resolution slightly different for old-style classes? — Marcin, Mar 14 '12 at 16:48
@Marcin: In this case, the method from `A` will be used in both versions. — Niklas B., Mar 14 '12 at 16:48
Without self as parameter of get, there is an error no? With version 2.7.2+ it raised an exception. — Jeremy D, Mar 14 '12 at 16:49
@Jeremy D:Yes it worked with self as the parameter for get().Thanks.. — Rajeev, Mar 14 '12 at 16:51

score 4 · Accepted Answer · answered Mar 14 '12 at 16:44

4

Well, it should be from class A. Because the search is depth-first, left-to-right.

answered Mar 14 '12 at 16:44

emirc

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In theory it should call A method but what is the error that i have mentioned.. – Rajeev Mar 14 '12 at 16:49
2

@Rajeev: You forgot to add the `self` parameter to the `get` methods. – Niklas B. Mar 14 '12 at 16:51
1

@Rajeev: Seeing that your question seems to be obsolete now, consider accepting this as an answer and get over with it. – Niklas B. Mar 14 '12 at 16:53
@Niklas B:I would have accepted the answer except.I had a timing constraint on the question.Thanks anyway – Rajeev Mar 14 '12 at 16:59

score 1 · Answer 2 · answered Mar 14 '12 at 16:52

First of all this code is inncorect as it does not have self variables within method declaration. Correct version is:

class A:
  def get(self):
    print "In A get"

class B:
  def get(self):
    print "In B get"

class C(A,B):
  def __init__(self):
    print "In c init"

c=C()
c.get()

Secondly this will print:

In c init
In A get

as ordering is defined in Method Resolution Order (MRO). Basicall class C will have all methods/attribues of B and then override by all mehods/attribues from A.

score 0 · Answer 3 · answered Mar 14 '12 at 16:52

0

The error you mentioned is clear: your methods are intended to thake a reference to their bound-to object, but they don't.

Change them to

def get(self):

as they are methods.

answered Mar 14 '12 at 16:52

glglgl

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score 0 · Answer 4 · answered Mar 14 '12 at 16:53

It'll be the A class method, like emirc say.

The error is given because you have to add self parameter to get definition, in that way:

class A:
 def get(self):
 print "In A get"

class B:
 def get(self):
 print "In B get"

class C(A,B):
 def __init__(self):
 print "In c init"

c=C()
c.get()

Python multiple inheritance property

4 Answers4