yn_prompt.py

#!/usr/bin/env python3
#
# Simple command line yes/no prompter.
# 2020-04-24 Jani Tammi <jasata@utu.fi>
#
#    default = None | "y" | "n"       If and how ENTER is interpreted.
#    echo = False | True              Will the prompt line be appended with selection.
#

def getch():
    """Read single character from standard input without echo."""
    import sys, tty, termios
    fd = sys.stdin.fileno()
    old_settings = termios.tcgetattr(fd)
    try:
        tty.setraw(sys.stdin.fileno())
        ch = sys.stdin.read(1)
    finally:
        termios.tcsetattr(fd, termios.TCSADRAIN, old_settings)
    return ch


# Python 3.6+
def yn_prompt(question: str, default=None, echo=False) -> bool:
    """Prompts a Yes/No question in console and returns True ("yes") or False ("no"). Second argument ("default") has three possible values; None, "n" or "y". Strings that cannot be interpreted are considered None. Default affects how ENTER keys are interpreted."""
    if default:
        # Empty string is False and will not branch here
        default = default[0].lower()
        if default not in ("n", "y"):
            default = None
            opts = "y/n"
        else:
            opts = ("y/N", "Y/n")[int(default == 'y')]
    else:
        default = None
        opts = "y/n"
    print(f"{question} ({opts}): ", end = "", flush = True)
    c = ""
    while c not in ("y", "n"):
        c = getch().lower()
        if ord(c) == 0x0d and default:
            selection = default == 'y'
            break
    selection = c == 'y'
    if echo:
        print(f"{('NO', 'YES')[int(selection)]}", flush = True)
    else:
        print("")
    return selection



if __name__ == "__main__":

    if yn_prompt("None?"):
        print("yes")
    else:
        print("no")

    if yn_prompt("empty string?", default="", echo=True):
        print("yes")
    else:
        print("no")

    if yn_prompt("gargage string?", default="garbage", echo=False):
        print("yes")
    else:
        print("no")

    if yn_prompt("yes?", default="YES", echo=True):
        print("yes")
    else:
        print("no")

    if yn_prompt("no?", default="NO", echo=True):
        print("yes")
    else:
        print("no")