Protocol: the keystone of type hints
summary
PEP 544 enables structural subtyping via typing.Protocol, letting static checkers verify duck‑typed interfaces. Uses typeshed annotations and mypy to reproduce a real bug in max, builds a Python reimplementation and iterates through failed attempts, then solves it with a bounded TypeVar plus a Protocol, writes six overloads, lands annotations that cover 14 standard‑library functions, and gets tests passing while mypy infers precise return types.
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chapters (8)
- 0:00Introduction to Protocols
- 2:08Static and Duck Typing
- 5:48Annotating the Max Function
- 10:44Using Numeric ABCs
- 15:43Restricted Type Variables
- 17:53Implementing Protocols
- 22:49Bounded Type Variables
- 25:18Embracing Gradual Typing
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