countdown

#!/usr/bin/env python
import os
import sys
import time
from datetime import datetime, timedelta

def display(string):
    sys.stderr.write('\r' + string + ' '*8 + '\b'*8)
    sys.stderr.flush()

def format_delta(delta, show_seconds=True, hours_always=False):
    s = ''
    if delta.days:
        s += str(delta.days) + ' '
        s += 'days ' if delta.days > 1 else 'day '

    hours = delta.seconds // 3600
    if hours or hours_always:
        s += "%d:" % hours

    s += "%02d" % ((delta.seconds // 60) % 60)

    seconds = delta.seconds % 60 + delta.microseconds / 1000000.
    if show_seconds:
        s += ':%02d' % round(seconds, 0)

    return s

def delta_in_seconds(delta):
    return delta.days * 86400 + delta.seconds + delta.microseconds / 1000000.

def countdown(delay):
    now = datetime.now()
    end = now + timedelta(seconds=delay)

    while now < end:
        display(format_delta(end - now))
        if end - now < timedelta(seconds=1):
            time.sleep(0.1)
        else:
            time.sleep(0.5)
        now = datetime.now()

    sys.stderr.write('\n')

def usage():
    sys.stderr.write('usage: %s SECONDS\n' % os.path.basename(sys.argv[0]))
    sys.exit(2)

if __name__ == '__main__':
    try:
        delay = int(sys.argv[1])
    except IndexError:
        usage()
    except ValueError:
        try:
            delay = float(sys.argv[1])
        except ValueError:
            usage()

    try:
        countdown(delay)
    except KeyboardInterrupt:
        sys.stderr.write('\n')
        sys.exit(130)