CODEWITHSUNDEEP
pythonsequence
Benjamin Naesen
Benjamin Naesen

Reputation: 172

Python: The sequence of inheritance?

In the example below, I've got 2 parent classes who initialize/declare the same variable. Why does it take the first class and not the second class? This is just for knowledge purposes.

class ParentClass:
    one = 'I am the first variable'
    two = 'I am the second variable'
    three = 'I am the thirt variable'


class ParentClass2:
    three = 'I am the third variable'


class ChildClass(ParentClass, ParentClass2):
    two = 'Different Text'
    pass

childObject = ChildClass()
parentObject = ParentClass()

print(parentObject.one)
print(parentObject.two)
print(childObject.one)
print(childObject.two)
print(childObject.three)

Output:

I am the first variable

I am the second variable

I am the first variable

Different Text

I am the thirt variable

Upvotes: 1

Views: 127

Answers (1)

Padraic Cunningham
Padraic Cunningham

Reputation: 180482

Because because ParentClass comes first in the mro 

 print(ChildClass.__mro__)
(<class '__main__.ChildClass'>, <class '__main__.ParentClass'>, <class '__main__.ParentClass2'>, <class 'object'>)

If you changed the order you would get the output you expect:

class ChildClass(ParentClass2,ParentClass):

(<class '__main__.ChildClass'>, <class '__main__.ParentClass2'>, <class '__main__.ParentClass'>, <class 'object'>)

Python checks from left to right for the attribute so because you have ParentClass first you get the attribute from the ParentClass class

Upvotes: 3

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