Miscellaneous

import sys
import re
from typing import Match, AnyStr, IO
 
# "typing.Match" describes regex matches from the re module
x: Match[str] = re.match(r'[0-9]+', "15")
 
# Use IO[] for functions that should accept or return any
# object that comes from an open() call (IO[] does not
# distinguish between reading, writing or other modes)
def get_sys_IO(mode: str = 'w') -> IO[str]:
    if mode == 'w':
        return sys.stdout
    elif mode == 'r':
        return sys.stdin
    else:
        return sys.stdout
 
# Forward references are useful if you want to reference a class before
# it is defined
def f(foo: A) -> int:  # This will fail
    ...
 
class A:
    ...
 
# If you use the string literal 'A', it will pass as long as there is a
# class of that name later on in the file
def f(foo: 'A') -> int:  # Ok
    ...