How to flush the input stream?

Question

I'm writing a simple alarm utility in Python.

#!/usr/bin/python

import time
import subprocess
import sys

alarm1 = int(raw_input("How many minutes (alarm1)? "))

while (1):
    time.sleep(60*alarm1)
    print "Alarm1"
    sys.stdout.flush()
    doit = raw_input("Continue (Y/N)?[Y]: ")
    print "Input",doit
    if doit == 'N' or doit=='n':
        print "Exiting....."
        break

I want to flush or discard all the key strokes that were entered while the script was sleeping and only accept the key strokes after the raw_input() is executed.

I'm running this on Windows XP.

Answer 1

From Rosetta Code

def flush_input():
    try:
        import msvcrt
        while msvcrt.kbhit():
            msvcrt.getch()
    except ImportError:
        import sys, termios    #for linux/unix
        termios.tcflush(sys.stdin, termios.TCIOFLUSH)

The try part is for Windows platform. I have not personally tested this part. But the except section works on linux terminal. termios module has some terminal interface functions. the tcflush can flush input or output buffered data. This part definitely works in my tests.

Answer 2

It would help to know what operating system you're using, as this is a very operating-system-specific question. For example, Kylar's answer doesn't work on Windows because sys.stdin doesn't have a fileno attribute.

I was curious and threw together a solution using curses, but this won't work on Windows either:

#!/usr/bin/python                                                               

import time
import sys
import curses

def alarmloop(stdscr):
    stdscr.addstr("How many seconds (alarm1)? ")
    curses.echo()
    alarm1 = int(stdscr.getstr())
    while (1):
        time.sleep(alarm1)
        curses.flushinp()
        stdscr.clear()
        stdscr.addstr("Alarm1\n")
        stdscr.addstr("Continue (Y/N)?[Y]:")
        doit = stdscr.getch()
        stdscr.addstr("\n")
        stdscr.addstr("Input "+chr(doit)+"\n")
        stdscr.refresh()
        if doit == ord('N') or doit == ord('n'):
            stdscr.addstr("Exiting.....\n")
            break

curses.wrapper(alarmloop)

EDIT: ah, Windows. Then you can use the msvcrt module. Note that the code below isn't perfect, and it doesn't work in IDLE at all:

#!/usr/bin/python

import time
import subprocess
import sys
import msvcrt

alarm1 = int(raw_input("How many seconds (alarm1)? "))

while (1):
    time.sleep(alarm1)
    print "Alarm1"
    sys.stdout.flush()

    # Try to flush the buffer
    while msvcrt.kbhit():
        msvcrt.getch()

    print "Continue (Y/N)?[Y]"
    doit = msvcrt.getch()
    print "Input",doit
    if doit == 'N' or doit=='n':
        print "Exiting....."
        break

Answer 3

On Unices, you can use termios.tcflush():

import time
import subprocess
import sys
from termios import tcflush, TCIOFLUSH

alarm1 = int(raw_input("How many minutes (alarm1)? "))

while (1):
    time.sleep(60*alarm1)
    print "Alarm1"
    sys.stdout.flush();
    tcflush(sys.stdin, TCIOFLUSH)
    doit = raw_input("Continue (Y/N)?[Y]: ")
    print "Input",doit
    if doit == 'N' or doit=='n':
        print "Exiting....."
        break

Answer 4

#!/usr/bin/python

import time
import subprocess
import sys
import os, select

alarm1 = int(raw_input("How many minutes (alarm1)? "))

while (1):
    time.sleep(3*alarm1)
    print "Alarm1"
    sys.stdout.flush()
    while select.select([sys.stdin.fileno()], [], [], 0.0)[0]:
        os.read(sys.stdin.fileno(), 4096)
    doit = raw_input("Continue (Y/N)?[Y]: ")
    print "Input",doit
    if doit == 'N' or doit=='n':
        print "Exiting....."
        break

Answer 5

Solution:

I have used (and worked in my case):

import sys

...
sys.stdin.flush()
...

Why this answer?

I have added this answer to this thread because I got here with the question "What was the syntax for flushing stdin?". I read the entries and thought that there had to be some flush method for stdin. I found it. I was surprised that it was not used in any entry and I thought that it should be.

Related documentation

• sys: https://docs.python.org/3.12/library/sys.html
• io: https://docs.python.org/3/library/io.html