Clear input buffer before input() on Windows?

I’m creating a game in which you have to guess the result of an operation in a certain time; to do this i created a thread to have a timed input and then I close the thread after the time is up.

Issue

My problem is that when the user doesn’t enter any number, before the time is up, in the next cycle the input waits for two inputs instead of one.

So, what I need is to clear the stdin before getting a new input. I find some solutions for Unix but nothing for Windows.

Code

import os
import random 
from time import sleep
import threading
import concurrent.futures

random.seed()

def get_input(a):
    a[0]=input()

def do_operation(time, n):
    number_1 = random.randint(0,n)
    number_2 = random.randint(0,n)
    operations = ['+', '-', '/', '*']
    operation = random.choices(operations)
    operation = "".join(operation)
    if operation == '/':
        while(number_1 % number_2 != 0):
            number_1 = random.randint(0,n)
            number_2 = random.randint(0,n)
    #Trovo i risultati delle operazioni
    if operation == '+':
        result = number_1 + number_2
    elif operation == '-':
        result = number_1 - number_2
    elif operation == '*':
        result = number_1 * number_2
    elif operation == '/':
        result = number_1 / number_2

    print(number_1,operation,number_2, '=', end = " ")
    count = [None, result]
    x = threading.Thread(target=get_input, args = (count,), daemon=True)
    x.start()
    x.join(time)
    return count


def stampastats(lives, points):
    print('nttttlives:', end = " ")

    for live in range(lives):
        print('*', end = " ")    

    print('nttttPoints:', points)

#main
lives = 3
points = 0
while(lives > 0):
    stampastats(lives, points)
    result = do_operation(10, 200)
    if result[0] != result[1]:
        print('nWrong')
        print('nThe result was: ' + str(result[1]))
        lives -= 1
    else:
        print('nBravo')
        points += 1000
    if lives == 0:
        print('nGAME OVER')
    else:
        sleep(1)
        os.system('cls')

Answer

There is a pending input() if a timeout happened. You can send an Enter in this case; I’m applying the pyautogui module to do that. (Call is_alive() after join() to decide whether a timeout happened.).

Some runtime errors fixed (and some debugging outputs kept) in the following script:

import os
import random 
from time import sleep
import threading
import concurrent.futures
import pyautogui

random.seed()

def get_input(a):
    a[0]=input()

def do_operation(time, n):
    number_1 = random.randint(0,n)
    number_2 = random.randint(0,n)
    operations = ['+', '-', '/', '*']
    operation = random.choices(operations)
    operation = "".join(operation)
    #Trovo i risultati delle operazioni
    if operation == '+':
        resulta = number_1 + number_2
    elif operation == '-':
        resulta = number_1 - number_2
    elif operation == '*':
        resulta = number_1 * number_2
    else: # operation == '/':
        while(number_2 == 0 or number_1 % number_2 != 0):
                number_1 = random.randint(0,n)
                number_2 = random.randint(0,n)
        resulta = number_1 / number_2
    
    print(number_1,operation,number_2, '=', end = " ")
    count = [None, resulta]
    x = threading.Thread(target=get_input, args = (count,), daemon=True)
    x.start()
    x.join(time)
    #print( x.native_id, x.is_alive(), x.isDaemon()) # debugging info 
    if x.is_alive():
        pyautogui.press("enter")               # answer to pending input()
    return count


def stampastats(lives, points):
    print('nttttlives:', end = " ")
    for live in range(lives):
        print('*', end = " ")    
    print('nttttPoints:', points)

#main
lives = 3
points = 0
while(lives > 0):
    stampastats(lives, points)
    result = do_operation(10, 200)
    #print(result)
    if((result[0] == None) or (result[0] == '') or (float(result[0]) != float(result[1]))):
        print('nWrong', result)
        print('The result was: ' + str(result[1]))
        lives -= 1
    else:
        print('nBravo', result)
        points += 1000
    if(lives == 0):
        print('nGAME OVER')
    else:
        sleep(1)
        # os.system('cls')