Interfaces [python-protocol] - Typescript to Python field guide

interfaces.py

from typing import Protocol, runtime_checkable


@runtime_checkable
class FileHandlerProtocol(Protocol):
    def open(self) -> bytes:
        ...

    def close(self) -> None:
        ...
 
# with usage like:

def get_contents(file_handler: FileHandlerProtocol) -> bytes:
    assert isinstance(file_handler, FileHandlerProtocol)
    try:
        return file_handler.open()
    finally:
        file_handler.close()

# implicitly implements the FileHandlerProtocol interface
class MyFile:
    def open(self) -> bytes:
        return b"hello"

    def close(self) -> None:
        return

contents = get_contents(MyFile()) # b"hello"