What is the Method Resolution Order (MRO)?

Question presented to candidate: "When a class inherits from several parents and two of them define the same method, how does Python decide which one runs? Walk me through the MRO, how it is computed, and how super() uses it."

What a strong answer should cover:

• The MRO is the single, ordered list of classes Python searches for an attribute; it is stored in Cls.__mro__ (also Cls.mro()), and the first class that defines the name wins.
• It is computed with the C3 linearization: a class comes before its parents, the left-to-right order of the bases is kept, every class appears once, and object is last.
• super() does not mean "my parent": it means "the next class after this one in the MRO of type(self)", which is what makes cooperative multiple inheritance (each method calling super()) run every class in a diamond exactly once.
• Some hierarchies have no consistent order; Python refuses them at class-creation time with TypeError: Cannot create a consistent method resolution order (MRO).
• Practical consequences: mixins go to the left of the main base, cooperative __init__ methods take **kwargs and pass the rest on, and C3 has been the rule since Python 2.3 (still the rule in Python 3).

Clarifying questions expected:

• Are we talking about method lookup on instances only, or also about how super() chains calls?

Code / implementation expected: Yes — a diamond hierarchy, its __mro__, and a super() chain that shows each class running once.