eastern_tzinfo.py

'''
tzinfo object to convert UTC datetime object to EST/EDT time

Can be used to convert datetime.now() from UTC to EST, e.g.
datetime.datetime.now(eastern_tzinfo())

Code modified from:
https://cloud.google.com/appengine/docs/python/datastore/typesandpropertyclasses?csw=1#datetime
'''

import datetime

class Eastern_tzinfo(datetime.tzinfo):
	"""Implementation of the Eastern timezone."""
	def utcoffset(self, dt):
		return datetime.timedelta(hours=-5) + self.dst(dt)

	def _FirstSunday(self, dt):
		"""First Sunday on or after dt."""
		return dt + datetime.timedelta(days=(6-dt.weekday()))

	def dst(self, dt):
		# 2 am on the second Sunday in March
		dst_start = self._FirstSunday(datetime.datetime(dt.year, 3, 8, 2))
		# 1 am on the first Sunday in November
		dst_end = self._FirstSunday(datetime.datetime(dt.year, 11, 1, 1))

		if dst_start <= dt.replace(tzinfo=None) < dst_end:
			return datetime.timedelta(hours=1)
		else:
			return datetime.timedelta(hours=0)
	def tzname(self, dt):
		if self.dst(dt) == datetime.timedelta(hours=0):
			return "EST"
		else:
			return "EDT"