Python read modifier keys (CTRL, ALT, SHIFT)

Question

this seems to be a hard one in Python..

I'm trying to read keystrokes and combinations with the modifier keys CTRL, ALT and SHIFT.

I'm on Python 2.7. It only has to work on Linux , but without X .

Currently, I can only read keystrokes using sys.stdin.read(), but the stdin.read() works like a file and doesn't give back the modifiers..

def getch():
    """getch() -> key character

    Read a single keypress from stdin and return the resulting character. 
    Nothing is echoed to the console. This call will block if a keypress 
    is not already available, but will not wait for Enter to be pressed. 

    If the pressed key was a modifier key, nothing will be detected; if
    it were a special function key, it may return the first character of
    of an escape sequence, leaving additional characters in the buffer.
    """
    fd = sys.stdin.fileno()
    old_settings = termios.tcgetattr(fd)
    try:
        tty.setraw(fd)
        ch = sys.stdin.read(1)
    finally:
        termios.tcsetattr(fd, termios.TCSADRAIN, old_settings)
    return ch

I'm flexible in the way the function returns the keystroke combination. First thing that comes to mind is to return maybe a list or a dict with the combination in it.. But main question is, how to detect it?!

Answer 1

Stdin, by definition is a stream of bytes representing control codes and characters. It is not a stream of key events. To get keys, you need to use an OS specific function. On Linux, the curses window objects have a getch methods. (There is something for Windows in another module.)

Tk, and Python's tkinter wrapper thereof, uses OS-specific methods to let one bind to both key press and release events, which include the modifiers you mention, in code that is mostly not OS specific.