How to make a file-like class work with "isinstance(cls, io.IOBase)"?

It seems that checking isinstance(..., io.IOBase) is the 'correct' way to determine if an object is 'file-like'.

However, when defining my own file-like class, it doesn't seem to work:

import io

class file_like():

    def __init__(self):
        pass

    def write(self, line):
        print("Written:", line)

    def close(self):
        pass

    def flush(self):
        pass

print(isinstance(file_like(), io.IOBase))
# Prints 'False'

How can I make it work?