Simple Python script for computing differences between times

timediff.py

#! /usr/bin/env python3

import argparse
import sys

from dateutil import parser as date_parser
from datetime import datetime

INTERVALS = (('years',   60 * 60 * 24 * 7 * 52),
             ('weeks',   60 * 60 * 24 * 7),
             ('days',    60 * 60 * 24),
             ('hours',   60 * 60),
             ('minutes', 60),
             ('seconds', 1))

def pretty_print_seconds(seconds):
    result = []
    for name, count in INTERVALS:
        value = seconds // count
        if value:
            seconds -= value * count
            if value == 1:
                name = name.rstrip('s')
            result.append('{} {}'.format(value, name))
    return ', '.join(result)

def main(argv):
    parser = argparse.ArgumentParser(description=('Enter any two times. If the '
        'second argument is ommitted, it is assumed to be the current time'))
    parser.add_argument('t1')
    parser.add_argument('t2', nargs='?')
    args = parser.parse_args(argv[1:])

    t1 = date_parser.parse(args.t1)

    if args.t2 is not None:
        t2 = date_parser.parse(args.t2)
    else:
        t2 = datetime.now()

    diff = (t2 - t1)

    print (pretty_print_seconds(int(diff.total_seconds())))

if __name__ == '__main__':
    sys.exit(main(sys.argv))