Unbuffered non-blocking keyboard input on command line

问题

I want to capture "all" keyboard input on the command line immediately (without waiting for a new line) in a non-blocking way.

This question demonstrates how you can read from stdin in a non-blocking way using select(). This is how it works:

while True:
    if select.select([sys.stdin], [], [], 0)[0] == [sys.stdin]:
        print(sys.stdin.read(1))

    ... do other stuff ...

Unfortunately you only get results after pressing RETURN.

My first guess was that stdin is just line buffered so after reading this question I turned my code into

ubuf_stdin = os.fdopen(sys.stdin.fileno(), 'rb', buffering=0)
while True:
    if select.select([ubuf_stdin], [], [], 0)[0] == [ubuf_stdin]:
        print(ubuf_stdin.read(1))
    ... do other stuff ...

This code works better - the buffer is being read completely without interruptions - but it still waits for RETURN being pressed.

I also tried to detach stdin:

ubuf_stdin = os.fdopen(sys.stdin.detach().fileno(), 'rb', buffering=0)

How do I react on keyboard input immediately after a key press?

回答1:

Use the getch module to get a single keypress at a time, as described in this question.

I don't think you'll be able to read stdin in a non-blocking-yet-character-at-a-time way, it's really not intended for that purpose.

回答2:

Ok this one does it but it has some disadvantages yet:

uses the curses module which seems a bit heavy to me
input has to be polled - no way to select() yet.
the keyboard input still gets printed to the terminal

.. but it works :).

import curses
def read_stdin(self):
    def cb(screen):
        result = []
        screen.nodelay(1)
        while True:
            try:
                result.append(screen.getkey())
            except curses.error:
                return result

    # contains a list of keys pressed since last call
    return curses.wrapper(cb)

来源：https://stackoverflow.com/questions/36066830/unbuffered-non-blocking-keyboard-input-on-command-line

标签

python

stdin

nonblocking