Python OOP tracing small confusion

Question

class GrandParent():
    def __init__(self, a, b):
        self._a = a
        self._b = b

    def blah(self):
        return "GP:" + self._a + self._b

class Parent2(GrandParent):
    def __init__(self, a, b, c):
        self._a = b
        self._b = a
        self._c = self.blah()

class Child2(Parent2):
    def __init__(self, a, b, c, d):    
        Parent2.__init__(self, a, b, c)

    def blah(self):
        return ("C2: " + self._a + self._b
        + self._c + self._d)


c2 = Child2("A", "B", "C", "D")

Here is the code I am supposed to trace. I create an object c2 of Child2. I go in Child2.__init__. I go in Parent2.__init__. I initialize self._a, self._b.

My problem is with self._c.

Parent2 does not have a blah() method, so I would expect it to get self._c from GrandParent.blah(), but instead it goes to the Child2.blah(). Why does this occur?

In your example Child2 needs to be a subclass of Parent2 (it currently says Parent1). The edit is too small for me to fix it. — p-robot
– p-robot, Commented Dec 10, 2016 at 1:46
@P-robot done, there were several other improvements that could be made so the edit was big enough. — Alex Hall
– Alex Hall, Commented Dec 10, 2016 at 1:50
Actually this is a code snippet part of something bigger, but the Parent1 did not play a factor, neither did classes like Child1, so I removed them because they weren't relevant to my problem — K Split X
– K Split X, Commented Dec 10, 2016 at 2:10

Alex Hall · Accepted Answer · 2016-12-10 01:44:18Z

1

Because self is a direct instance of Child2 so self.blah() must be the equivalent of Child2.blah(self). That the code happens to be in a method of a parent of Child2 just before that call is not relevant.

answered Dec 10, 2016 at 1:44

Alex Hall

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2 Comments

K Split X Over a year ago

Ohhhh .... but in the case that Child2 did not ahve blah , then would it call the parent?

Alex Hall Over a year ago

Yes. More specifically it will look through Child2.__mro__ (method resolution order) and pick the first one that has the method.

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