non-blocking getch() in curses

Question

How can I use getch() function in curses in a non-blocking way?

    while True:
        x.addstr('Press any key to load menu')
        x.getch()
        x.clear()
        x.refresh()
        menu()
        type = x.getch()  # BLOCKING - I want it to be non-blocking

Answer 1

I'm assuming you are on *nix machine like mac or a linux distro. Here is a non-blocking way to dump keys that are in keyboard buffer but have not been read yet. Does not require using curses.

Returns either a string with single printable character, or a longer string with ANSI escape sequence for more complex key-combos, or empty string to avoid blocking if there is nothing to read.

You can comment out the tty.setraw without making other changes if you wish to have the read be cooked text as opposed to raw text. This mainly affects how special characters like ctrl+c are treated.

def non_block_getch():
    old_settings = termios.tcgetattr(sys.stdin.fileno()) # save settings
    tty.setraw(sys.stdin.fileno()) # raw to read single raw key w/o enter
    os.set_blocking(sys.stdin.fileno(), False) # dont block for empty buffer
    buffer_dump = ""
    while char := sys.stdin.read(1):
        buffer_dump += char
    os.set_blocking(sys.stdin.fileno(), True) # restore normal settings
    termios.tcsetattr(sys.stdin.fileno(), termios.TCSANOW, old_settings)
    if buffer_dump:
        return buffer_dump
    else:
        return ""

For windows you can use these constructs to hopefully solve the problem.

import msvcrt
mscvrt.kbhit() # will report True/False depending if there is something in buffer

Unfortunately if you use msvcrt.wgetch() for better compability, the kbhit function won't work properly.

I suggest using the following:

def non_block_w_getch():
    try:
        msvcrt.ungetwch("a")
    except OSError:
        return msvcrt.getwch()
    else:
        _ = msvcrt.getwch()
        return ""

The ungetch will fail if and only if there is something in the buffer, so in the case of OSError being raised there is something to be read immediately, hence we return msvcrt.getwch() which will not block for this occasion.

If there is no fail, the else section will clear the ungetch and discard it after which we return "" to avoid blocking and to indicate that there was nothing to read