timezone validator

LocalDateTime.py

class LocalDateTime(formencode.FancyValidator):
	""" This class is a formencode validator that will localize a date-time.

	By default python date-time objects don't have any time zone information
	associated with them, but they provide abstract support for time zones.
	The pytz module provides concrete timezones to use with date-time objects.

	This class will ensure that all dates have a timezone associated with them.
	It will wite dates to the DB with the UTC time zone; it will convert dates
	read from the DB to the client's local time zone defined in their config 
	file.

	"""
	# This time zone should be read from the client's config file.
	# I'm just faking it for now.
	tz = 'US/Eastern' 

	timezone = pytz.timezone(tz)
	utc = pytz.UTC
	
	def _to_python(self, value, state):
		""" This method will transform the value before it gets read from the DB.
		"""
		if value.tzinfo:
			return value.astimezone(self.timezone)
		else:
			return self.utc.localize(value).astimezone(self.timezone)

	def _from_python(self, value, state):
		""" This method will transform the value before it gets written to the DB. 
		"""
		return self.timezone.localize(value).astimezone(self.utc)


# Use this validator in our models like so

class ProposalStepAction(SQLObject):

	proposalStep = ForeignKey('ProposalStep')
	user = ForeignKey('User')

	created = DateTimeCol(default=None, validator=LocalDateTime)
	modified = DateTimeCol(default=None, validator=LocalDateTime)
	opened = DateTimeCol(default=None, validator=LocalDateTime)
	signature = DateTimeCol(default=None, validator=LocalDateTime)
        # ...