from datetime import datetime
import dateutil.parser
a = datetime.now()
#a = datetime.strftime(a, format="%Y-%m-%d%H:%M:%S")
#a = a[:10] + 'T' + a[10:] + 'Z'
a = datetime.strftime(a, format="%Y-%m-%dT%H:%M:%SZ")
a = dateutil.parser.parse(a) - dateutil.parser.parse("2018-09-29T00:33:33Z")
print(str(a))
3 days, 2:00:00