Calculate timestamps by adding or subtracting seconds

timestamp.py

#!/usr/bin/python3

import sys
import re
from datetime import datetime, timedelta

if not len(sys.argv) == 4:
    print('\n * usage: ' + sys.argv[0] + ' %Y-%m-%d-%H:%M[:%S] add|sub #seconds\n')
    exit(1)

start_date = sys.argv[1]
action = sys.argv[2]
seconds = int(sys.argv[3])

difference = timedelta(seconds=seconds)

pattern_with_seconds = re.compile("^[0-9]{4}-[0-9]{2}-[0-9]{2}-[0-9]{2}:[0-9]{2}:[0-9]{2}$")
pattern_without_seconds = re.compile("^[0-9]{4}-[0-9]{2}-[0-9]{2}-[0-9]{2}:[0-9]{2}$")

if re.match(pattern_with_seconds, start_date):
    source_date =  datetime.strptime(start_date, '%Y-%m-%d-%H:%M:%S')
elif re.match(pattern_without_seconds, start_date):
    source_date =  datetime.strptime(start_date, '%Y-%m-%d-%H:%M')
else:
    print('wrong timestamp format')
    exit(1)

print('\nGiven timestamp: ' + start_date, end =" ")

if action == 'add':
    result_date = source_date + timedelta(seconds = seconds)
    print('+', end =" ")
elif action == 'sub':
    result_date = source_date - timedelta(seconds = seconds)
    print('-', end =" ")

print(str(seconds) + ' = ' + str(result_date) + ' (Difference ' + str(difference) + ')' + '\n')

#
# EXAMPLES:
#
# $ ./timestamp.py
#
# * usage: ./test.py %Y-%m-%d-%H:%M[:%S] add|sub #seconds
#
#
# $ ./timestamp.py 2021-04-17-12:17:20 add 4700
#
# Given timestamp: 2021-04-17-12:17:20 + 4700 = 2021-04-17 13:35:40 (Difference 1:18:20)
#
#
# $ ./timestamp.py 2021-04-17-12:17:20 sub 65400
#
# Given timestamp: 2021-04-17-12:17:20 - 65400 = 2021-04-16 18:07:20 (Difference 18:10:00)
#
#
# $ ./timestamp.py 2021-04-17-12:17 add 88423
#
# Given timestamp: 2021-04-17-12:17 + 88423 = 2021-04-18 12:50:43 (Difference 1 day, 0:33:43)
#
#
# $ ./timestamp.py 2021-04-17-12:17 sub 18402739
#
# Given timestamp: 2021-04-17-12:17 - 18402739 = 2020-09-16 12:24:41 (Difference 212 days, 23:52:19)
#