Countdown timer starts from `start_value` and counts down to zero, then counts up with negated time. Only displays minutes and seconds. No pause or reset available.

countdown_timer.py

import time
from threading import Timer


def now():
    """ Return the current time in seconds since the epoch. """
    return int(time.time())


class Countdown(object):
    """
    Countdown timer starts immediatly on init from `start_value` and counts down
    to zero, then counts up with negated time. Only displays minutes and
    seconds. No pause or reset available. Each "tick" of the clock is passed to
    the callback function as a string. """
    
    def __init__(self, start_value, callback):
        self._finished = False
        self.start_value = start_value
        self.callback = callback
        self.start_time = now()
        self._update()

    def _update(self):
        self._set_time(now() - self.start_time)
        if not self._finished:
            self._timer = Timer(1, self._update)
            self._timer.start()

    def _set_time(self, value):
        neg = '' 
        if self.start_value > value:
            value = self.start_value - value
        elif self.start_value < value:
            value = value - self.start_value
            neg = '-'
        else:
            value = 0
        mm, ss = divmod(value, 60)
        self.callback("{}{:02d}:{:02d}".format(neg, mm, ss))

    def stop(self):
        self._timer.cancel()
        self._finished = True


if __name__ == '__main__':
    from sys import stdout, argv
    
    # Codes are here: http://www.termsys.demon.co.uk/vtansi.htm
    RED, GREEN, YELLOW = 31, 32, 33

    def callback(t):
        """ Replace previous string written to console with new string. """
        color = RED if t.startswith('-') else YELLOW if t.startswith('00') else GREEN
        stdout.write('\rCountdown: \033[{0};1m{1}\033[0m'.format(color, t.lstrip('-')))
        stdout.flush()

    if len(argv) > 1:
        for arg in argv[1:]:
            mm, ss = arg.split(':')
            c = Countdown((int(mm) * 60) + int(ss), callback)
    
            raw_input('    Press [enter] to stop.')
            c.stop()
    
    else:
        print 'No time provided to count down from. Use `mm:ss`.'