Method Resolution Order

Method Resolution Order (MRO) is the sequence Python follows to search for a method or attribute across a class and its parent classes - especially important to understand when a class uses multiple inheritance.

Why MRO Matters

When a class inherits from more than one parent, and multiple parents define a method with the same name, Python needs a clear, consistent rule to decide which version actually gets called. That rule is the MRO.

class A:
    def greet(self):
        print("Hello from A")

class B(A):
    def greet(self):
        print("Hello from B")

class C(A):
    def greet(self):
        print("Hello from C")

class D(B, C):
    pass

d = D()
d.greet()   # Hello from B

Checking the MRO

You can inspect the exact resolution order Python will follow using the mro() method or the __mro__ attribute.

print(D.mro())
# [D, B, C, A, object]

Python uses an algorithm called C3 linearization to compute this order, which ensures a consistent, predictable search path: it checks the class itself first, then its parents left to right, without ever checking a parent before one of its own children.

Coming Up Next

Next, you'll learn about Overloading - how Python handles methods and operators that need to behave differently depending on their input.