tzutils.py

# encoding: utf-8
import pytz
import datetime
from django.utils import timezone

"""
campus is a django model
for these examples:

campus.tz = 'America/Denver'
naivetime = datetime.time(15, 00)

I am getting datetime.time(16, 00) which != datetime.time(15, 00)
when I run the following:
>>> naivetime = datetime.time(15, 00)
>>> utctime = campus_time_to_utc(campus, naivetime)
>>> campus_time = utc_time_to_campus(campus, utctime)
>>> naivetime == campus_time
→ returns False
"""

def campus_time_to_utc(campus, naivetime):
    """
    based on a campus and a naive time, 
    convert the time to a naive utc for saving
    """
    just_time = False
    stdtime = timezone.datetime(2014, 01, 01, 00, 00)
    utc = pytz.timezone('UTC')
    tz = pytz.timezone(campus.tz)
    # we can't associate time to tz without knowing the date
    # this is due to dst
    # we can assume that if this fx is being called, then
    # the dst is based on a standard date and combine
    if type(naivetime) == datetime.time:
        naivetime = timezone.datetime.combine(stdtime, naivetime)
        just_time = True
    tztime = tz.localize(naivetime)
    utctime = utc.normalize(tztime)
    if just_time:
        return utctime.replace(tzinfo=None).time()
    return utctime.replace(tzinfo=None)


def utc_time_to_campus(campus, utctime):
    """
    based on a campus and a stored naive utc time
    return the local timezone-aware time 
    returns time if only receiving a datetime.time
    """
    just_time = False
    stdtime = timezone.datetime(2014, 01, 01, 00, 00)
    utc = pytz.timezone('UTC')
    tz = pytz.timezone(campus.tz)

    if type(utctime) == datetime.time:
        utctime = timezone.datetime.combine(stdtime, utctime)
        just_time = True
    utctime = utctime.replace(tzinfo=utc)
    campus_time = tz.normalize(utctime)
    if just_time:
        return campus_time.time()
    return campus_time