Protocol

Use Python Protocols for Structural Typing at API Boundaries

Python often relies on duck typing: if an object supports the operation a function needs, its concrete class does not matter. typing.Protocol gives static type checkers a way to describe that idea explicitly without requiring implementations to inherit from a shared base class. Define the behavior you consume from typing import Protocol class ByteWriter(Protocol): def write(self, data: bytes) -> int: ... def emit_header(writer: ByteWriter) -> None: writer.write(b"NLR1") Any statically compatible object can satisfy ByteWriter, even if its class never mentions the protocol.