python datetime

import datetime as DT

#convert character string: '20150212 10:12:11' to datetime type: pTime
pTime = DT.datetime.strptime('20150212 10:12:11', '%Y%m%d %H:%M:%S')

#calculate the number of days between two date：utcnow() and pTime
days = (  DT.datetime.utcnow()-  pTime  ).days

#day of the year
DOY = (  pTime- DT.datetime(pTime.year, 1, 1) ).days+1

#calculate the time after 1h
aftTime = pTime+ DT.timedelta(hours=1)