Classes and Protocols

Building classes that feel like built-in types is the goal of this part. Python’s standard library is a long argument that good class design is about implementing the right protocols — not inheriting from the right base class.

• 23  A Pythonic Object is a single example carried through five sections: a Vector2d class that becomes printable, hashable, formattable, slottable, and private-aware. It’s the chapter where every special method finally meets a use case.

• 24  Special Methods for Sequences extends that example to a multi-dimensional Vector, implementing the full sequence protocol — __getitem__, __len__, slicing, formatting, hashing — so the object behaves like tuple.

• 25  Interfaces, Protocols, and ABCs draws the line between Python’s two type systems. Nominal typing (you inherit from an ABC) and structural typing (you implement the right methods) coexist. We’ll write a Vowel class twice, once each way, and see which is more Pythonic.

• 26  Inheritance: For Better or for Worse is the cautionary chapter. The MRO, mixins, multiple inheritance, the diamond — all of it works, none of it is required. Most Python code reaches for composition first, and you should too.

• 27  More About Type Hints returns to type hints with the tools that matter at scale: TypeVar, Generic, Protocol, overload, TypedDict. These are the hints that catch bugs you’d otherwise ship.