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from typing import Protocol, runtime_checkable


@runtime_checkable
class Closeable(Protocol):
    def close(self) -> None: ...


class File:
    def close(self):
        return "file"


class Bag:
    pass


class Stream:
    """Doesn't inherit Closeable; still passes by structural matching."""
    def close(self):
        return "stream"


class Weird:
    """Has a 'close' attribute, but it's an int."""
    close = 42


print(isinstance(File(), Closeable))
print(isinstance(Bag(), Closeable))
print(isinstance(Stream(), Closeable))
print(isinstance(Weird(), Closeable))

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