Python argument type specification for files

Question

I know, for example, that a function can be written to let know its argument is str:

def myfunc(s: str) -> None:

I search the documentation of typing but couldn't find anything about files as arguments.

How can I specify something as the following:

def use_file(a_file: ???) -> None:

where ??? is a binary file (as one created with open("data", "rb"))?

Answer 1

The typing module provides specific types for file-like objects. Your question is a duplicate of this question.

from typing import IO, TextIO, BinaryIO

# Answer to the question
# If your function only accepts files opened in binary mode 
def use_file(a_file: BinaryIO) -> None:
    ...

# If your function only accepts files opened in text mode
def use_file(a_file: TextIO) -> None:
    ...

# If your function accepts files opened in both modes
def use_file(a_file: IO) -> None:
    ...