The correct way to annotate a “file type” in Python [duplicate]

You can use typing.IO, typing.TextIO, and typing.BinaryIO to represent different types of I/O streams. To quote the documentation:

сlass typing.IO
class typing.TextIO
class typing.BinaryIO

Generic type IO[AnyStr] and its subclasses TextIO(IO[str]) and BinaryIO(IO[bytes]) represent the types of I/O streams such as
returned by open().