Method resolution order and cooperative super()

Intermediate Python OOP Inheritance

Created by Pavel · 07.03.2026 at 19:57 UTC · 3 completed

Multiple inheritance forces a single, deterministic rule for which parent implementation runs when several paths meet. Python's MRO is that rule; ClassName.__mro__ shows the lookup tuple, and super() follows it so cooperative __init__ chains do not call Base twice in the diamond pattern.

In practice you log or trace construction when debugging framework code. The edge case is assuming super() means “call the parent” literally—it means “call the next class in the MRO,” which can be a sibling branch before the common base.

University approvals: 0

Tasks

Question 1

Which attribute shows the inheritance search order of a class?

Hint

It's a tuple of classes

bases

mro

mro_order

parents

Question 2

Implement the diamond with cooperative super() exactly as specified (names must match).

Base.__init__ sets self.log = ["Base"].
Left(Base).__init__ calls super().__init__() then self.log.append("Left").
Right(Base).__init__ calls super().__init__() then self.log.append("Right").
Diamond(Left, Right).__init__ calls super().__init__() then self.log.append("Diamond").
After d = Diamond(), assert d.log equals ['Base', 'Right', 'Left', 'Diamond'] (CPython 3 ordering).

Submit the full script. Tests use expression mode on your globals after execution.

Hint

Use super() in every init; do not call Base.init directly.

class Base:
    def __init__(self):
        # TODO: set self.log to ["Base"]
        pass


class Left(Base):
    def __init__(self):
        # TODO: super then append "Left"
        pass


class Right(Base):
    def __init__(self):
        # TODO: super then append "Right"
        pass


class Diamond(Left, Right):
    def __init__(self):
        # TODO: super then append "Diamond"
        pass

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Card Info

Topic: Python OOP Inheritance
Difficulty: Intermediate
Completed: 3 users

Creator

Pavel