时间限制输入？

Question

我想要做的是通过输入向用户提问。例如：

print('some scenario')
prompt = input("You have 10 seconds to choose the correct answer...\n")

然后如果时间到了，就打印出类似这样的内容：

print('Sorry, times up.')

如果有人能帮我指点一下方向，我会非常感激。

Answer 1

如果在用户没有提供答案的情况下，阻塞主线程是可以接受的：

from threading import Timer

timeout = 10
t = Timer(timeout, print, ['Sorry, times up'])
t.start()
prompt = "You have %d seconds to choose the correct answer...\n" % timeout
answer = input(prompt)
t.cancel()

否则，你可以参考@Alex Martelli的回答（这个回答是针对Python 3修改过的），适用于Windows（但没有经过测试）：

import msvcrt
import time

class TimeoutExpired(Exception):
    pass

def input_with_timeout(prompt, timeout, timer=time.monotonic):
    sys.stdout.write(prompt)
    sys.stdout.flush()
    endtime = timer() + timeout
    result = []
    while timer() < endtime:
        if msvcrt.kbhit():
            result.append(msvcrt.getwche()) #XXX can it block on multibyte characters?
            if result[-1] == '\r':
                return ''.join(result[:-1])
        time.sleep(0.04) # just to yield to other processes/threads
    raise TimeoutExpired

用法：

try:
    answer = input_with_timeout(prompt, 10)
except TimeoutExpired:
    print('Sorry, times up')
else:
    print('Got %r' % answer)

在Unix系统上你可以尝试：

import select
import sys

def input_with_timeout(prompt, timeout):
    sys.stdout.write(prompt)
    sys.stdout.flush()
    ready, _, _ = select.select([sys.stdin], [],[], timeout)
    if ready:
        return sys.stdin.readline().rstrip('\n') # expect stdin to be line-buffered
    raise TimeoutExpired

或者：

import signal

def alarm_handler(signum, frame):
    raise TimeoutExpired

def input_with_timeout(prompt, timeout):
    # set signal handler
    signal.signal(signal.SIGALRM, alarm_handler)
    signal.alarm(timeout) # produce SIGALRM in `timeout` seconds

    try:
        return input(prompt)
    finally:
        signal.alarm(0) # cancel alarm

Answer 2

这是个有趣的问题，似乎这个方法可以解决：

import time
from threading import Thread

answer = None

def check():
    time.sleep(2)
    if answer != None:
        return
    print("Too Slow")

Thread(target = check).start()

answer = input("Input something: ")