Type hint for a file or file-like object?

Question

Is there any correct type hint to use for a file or file-like object in Python? For example, how would I type-hint the return value of this function?

def foo():
         


        

Answer 1

The short answer:

• You need to be explicit. That is from typing import TextIO not just from typing import *.
• Use IO to mean a file without specifying what kind
• Use TextIO or BinaryIO if you know the type
• You cannot currently specify it be opened for write or its encoding.

As an example:

from typing import BinaryIO

def binf(inf: BinaryIO):
    pass

with open('x') as f:
    binf(f)

gives an inspection error (in PyCharm) of Expected type 'BinaryIO', got 'TextIO' instead