Taking in multiple inputs for a fixed time

This solution is platform-independent and immediately interrupts typing to inform about an existing timeout. It doesn't have to wait until the user hits ENTER to find out a timeout occured. Besides informing the user just-in-time this ensures no input after the timeout stepped in is further processed.

Features

• Platform independent (Unix / Windows).
• StdLib only, no external dependencies.
• Threads only, no Subprocesses.
• Immediate interrupt at timeout.
• Clean shutdown of prompter at timeout.
• Unlimited inputs possible during time span.
• Easy expandable PromptManager class.
• Program may resume after timeout, multiple runs of prompter instances possible without program restart.

This answer uses a threaded manager instance, which mediates between a separate prompting thread and the MainThread. The manager-thread checks for timeout and forwards inputs from the prompt-thread to the parent-thread. This design enables easy modification in case MainThread would need to be non-blocking (changes in _poll to replace blocking queue.get()).

On timeout the manager thread asks for ENTER to continue and uses an threading.Event instance to assure the prompt-thread shuts down before continuing. See further details in the doc-texts of the specific methods:

from threading import Thread, Event
from queue import Queue, Empty
import time


SENTINEL = object()


class PromptManager(Thread):

    def __init__(self, timeout):
        super().__init__()
        self.timeout = timeout
        self._in_queue = Queue()
        self._out_queue = Queue()
        self.prompter = Thread(target=self._prompter, daemon=True)
        self.start_time = None
        self._prompter_exit = Event()  # synchronization for shutdown
        self._echoed = Event()  # synchronization for terminal output

    def run(self):
        """Run in worker-thread. Start prompt-thread, fetch passed
        inputs from in_queue and check for timeout. Forward inputs for
        `_poll` in parent. If timeout occurs, enqueue SENTINEL to
        break the for-loop in `_poll()`.
        """
        self.start_time = time.time()
        self.prompter.start()

        while self.time_left > 0:
            try:
                txt = self._in_queue.get(timeout=self.time_left)
            except Empty:
                self._out_queue.put(SENTINEL)
            else:
                self._out_queue.put(txt)
        print("\nTime is out! Press ENTER to continue.")
        self._prompter_exit.wait()

    @property
    def time_left(self):
        return self.timeout - (time.time() - self.start_time)

    def start(self):
        """Start manager-thread."""
        super().start()
        self._poll()

    def _prompter(self):
        """Prompting target function for execution in prompter-thread."""
        while self.time_left > 0:
            self._in_queue.put(input('>$ '))
            self._echoed.wait()  # prevent intermixed display
            self._echoed.clear()

        self._prompter_exit.set()

    def _poll(self):
        """Get forwarded inputs from the manager-thread executing `run()`
        and process them in the parent-thread.
        """
        for msg in iter(self._out_queue.get, SENTINEL):
            print(f'you typed: {msg}')
            self._echoed.set()
        # finalize
        self._echoed.set()
        self._prompter_exit.wait()
        self.join()


if __name__ == '__main__':

    pm = PromptManager(timeout=5)
    pm.start()

Example Output:

>$ Hello
you typed: Hello
>$ Wor
Time is out! Press ENTER to continue.

Process finished with exit code 0

Note the timeout-message here popped up during the attempt of typing "World".

You can use the poll() method (tested on Linux):

import select,sys

def timed_input(sec):

    po= select.poll()   # creating a poll object
    # register the standard input for polling with the file number 
    po.register(sys.stdin.fileno(), select.POLLIN)  

    while True:
        # start the poll
        events= po.poll(sec*1000)   # timeout: milliseconds
        if not events:
            print("\n Sorry, it's too late...")
            return ""

        for fno,ev in events:     #  check the events and the corresponding fno  
            if fno == sys.stdin.fileno():  # in our case this is the only one
                return(input())


s=timed_input(10)
print("From keyboard:",s)  

The stdin buffers the pressed keys, and the input() function read that buffer at once.