datetime library use

library_datetime.py

"""
class datetime.date
  An idealized naive date, assuming the current Gregorian calendar always was, and always will be, in effect. 
  Attributes: year, month, and day.

class datetime.time
  An idealized time, independent of any particular day, assuming that every day has exactly 24*60*60 seconds (there is no notion of “leap seconds” here). 
  Attributes: hour, minute, second, microsecond, and tzinfo.

class datetime.datetime
  A combination of a date and a time. 
  Attributes: year, month, day, hour, minute, second, microsecond, and tzinfo.

class datetime.timedelta
  A duration expressing the difference between two date, time, or datetime instances to microsecond resolution.

class datetime.tzinfo
  An abstract base class for time zone information objects. These are used by the datetime and time classes to provide a customizable notion of time adjustment (for example, to account for time zone and/or daylight saving time).
"""


from datetime import datetime

# CREATE DATETIME OBJECT
date1 = datetime(2011, 4, 1) # 2011-04-01 00:00:00
datetime1 = datetime(2011, 4, 1, 16, 8, 18, 445529) # 2011-04-01 16:08:18.445529
now = datetime.now() # current datetime

# DATETIME OBJECT TO STRING
sdate1 = date1.strftime("%Y-%m-%d %H:%M:%S") # FORMAT: https://docs.python.org/2/library/datetime.html#strftime-and-strptime-behavior

# DATE STRING TO DATETIME OBJECT
date = datetime.strptime(sdate, '%Y-%m-%dT%H:%M:%SZ')

# numpy.datetime64 TO DATETIME OBJECT
date = pd.Timestamp(datenp64).to_pydatetime()

# ADD STEP TO DATETIME OBJECT
from datetime import datetime,timedelta

date1 = datetime(2014,1,1)
date2 = date1 + timedelta(days=2)
print date1,date2 # 2014-01-01 00:00:00 2014-01-03 00:00:00

# TIMEDELTA OBJECT TO NUMBER
td = date2 - date1
days, hours, minutes = td.days, td.seconds // 3600, td.seconds // 60 % 60

## CREATE LIST OF DATETIME OBJECT BETWEEN TWO DATETIMES
# Monthly
def months_between(start,end):
    from datetime import datetime,timedelta
    months = []
    cursor = start

    while cursor <= end:
        newcursor = datetime(cursor.year,cursor.month,1)
        if newcursor not in months:
            months.append(newcursor)
        cursor += timedelta(weeks=1)

    newcursor = datetime(cursor.year,cursor.month,1)
    months.append(newcursor)

    return months
    
# Daily
ldatetimes = [ datei+timedelta(days=iday) for iday in range((datef-datei).days+1)]
# Hourly
ldatetimes = [ datei+timedelta(hours=ihour) for ihour in range(((datef-datei).days+1)*24)]
# 10 minutes 
l10dt = [ dti+timedelta(seconds=i10min*10.*60.) for i10min in range(int(int((dtf-dti).total_seconds()/60.)/10.)+1)]

## UTC TO LOCAL TIME
from datetime import datetime
from dateutil import tz
# METHOD 1: Hardcode zones:
from_zone = tz.gettz('UTC')
to_zone = tz.gettz('America/New_York')
# METHOD 2: Auto-detect zones:
from_zone = tz.tzutc()
to_zone = tz.tzlocal()
# utc = datetime.utcnow()
utc = datetime.strptime('2011-01-21 02:37:21', '%Y-%m-%d %H:%M:%S')
# Tell the datetime object that it's in UTC time zone since 
# datetime objects are 'naive' by default
utc = utc.replace(tzinfo=from_zone)
# Convert time zone
central = utc.astimezone(to_zone)


# calculate temporal resolution for a list of dates (in minutes)
tresol = int(np.mean([int((idate - ldates[i]).seconds/60.) for i,idate in enumerate(ldates[1:])]))


## combine date and time object
from datetime import datetime
datetime.combine(datetime.date(2011, 1, 1), datetime.time(10, 23))