"Python Method Resolution Order (MRO), Explained Simply"
"Python method resolution order is the hidden lookup list behind every attribute access. Learn how C3 linearization builds it, why super() surprises you, and how to fix the dreaded inconsistent-MRO TypeError."
Here's the lie every Python tutorial lets you keep: super() calls your parent class. It doesn't. super() calls the *next class in the method resolution order* — and in multiple inheritance, that next class is frequently a sibling you've never heard of. Python method resolution order (MRO) is the invisible list Python consults for every attribute lookup, and once you can read it, inheritance stops being spooky. This guide proves the super() surprise with runnable code, walks the C3 algorithm step by step, and fixes the infamous inconsistent-MRO TypeError . What you'll learn What the MRO is and how to inspect it with __mro__ and .mro() Why the diamond problem resolves to exactly one order How C3 linearization builds that order, merge step by merge step Why super() in one class can invoke a *sibling* class — and why that's correct The cooperative **kwargs pattern for __init__ chains How to read an MRO when debugging, and how to fix inconsistent hierarchies Python method resolution order in one sentence The MRO is the ordered list of classes Python searches — left to right — when you access an attribute, and the first class that has it wins. Every class carries this list. Print it: class A: pass class B(A): pass class C(A): pass class D(B, C): pass print(D.__mro__) # (<class '__main__.D'>, <class '__main__.B'>, <class '__main__.C'>, # <class '__main__.A'>, <class 'object'>) print([c.__name__ for c in D.mro()]) # ['D', 'B', 'C', 'A', 'object'] __mro__ is the tuple; .mro() returns the same order as a list. The practical consequence: when you write d.label and both B and C define label , B wins — not because B is "more of a parent," but because B appears…