Fixed #10048 -- Handle non-existent timezone in dateformat functions.

    def I(self):

        "'1' if Daylight Savings Time, '0' otherwise."

        if self.timezone.dst(self.data):

        if self.timezone and self.timezone.dst(self.data):

            return u'1'

        else:

            return u'0'

    def T(self):

        "Time zone of this machine; e.g. 'EST' or 'MDT'"

        name = self.timezone.tzname(self.data)

        name = self.timezone and self.timezone.tzname(self.data) or None

        if name is None:

            name = self.format('O')

        return unicode(name)

    def U(self):

        "Seconds since the Unix epoch (January 1 1970 00:00:00 GMT)"

        off = self.timezone.utcoffset(self.data)

        off = self.timezone and self.timezone.utcoffset(self.data) or 0

        return int(time.mktime(self.data.timetuple())) + off.seconds * 60

    def w(self):

        timezones west of UTC is always negative, and for those east of UTC is

        always positive.

        """

        if not self.timezone:

            return 0

        offset = self.timezone.utcoffset(self.data)

        # Only days can be negative, so negative offsets have days=-1 and

        # seconds positive. Positive offsets have days=0