Class DstTzInfo

tests/test_code/py/pytz/tzinfo.py:156–526

A timezone that has a variable offset from UTC The offset might change if daylight saving time comes into effect, or at a point in history when the region decides to change their timezone definition.

class DstTzInfo(BaseTzInfo):
    '''A timezone that has a variable offset from UTC

    The offset might change if daylight saving time comes into effect,
    or at a point in history when the region decides to change their
    timezone definition.
    '''
    # Overridden in subclass

    # Sorted list of DST transition times, UTC
    _utc_transition_times = None

    # [(utcoffset, dstoffset, tzname)] corresponding to
    # _utc_transition_times entries
    _transition_info = None

    zone = None

    # Set in __init__

    _tzinfos = None
    _dst = None  # DST offset

    def __init__(self, _inf=None, _tzinfos=None):
        if _inf:
            self._tzinfos = _tzinfos
            self._utcoffset, self._dst, self._tzname = _inf
        else:
            _tzinfos = {}
            self._tzinfos = _tzinfos
            self._utcoffset, self._dst, self._tzname = (
                self._transition_info[0])
            _tzinfos[self._transition_info[0]] = self
            for inf in self._transition_info[1:]:
                if inf not in _tzinfos:
                    _tzinfos[inf] = self.__class__(inf, _tzinfos)

    def fromutc(self, dt):
        '''See datetime.tzinfo.fromutc'''
        if (dt.tzinfo is not None and
                getattr(dt.tzinfo, '_tzinfos', None) is not self._tzinfos):
            raise ValueError('fromutc: dt.tzinfo is not self')
        dt = dt.replace(tzinfo=None)
        idx = max(0, bisect_right(self._utc_transition_times, dt) - 1)
        inf = self._transition_info[idx]
        return (dt + inf[0]).replace(tzinfo=self._tzinfos[inf])

    def normalize(self, dt):
        '''Correct the timezone information on the given datetime

        If date arithmetic crosses DST boundaries, the tzinfo
        is not magically adjusted. This method normalizes the
        tzinfo to the correct one.

        To test, first we need to do some setup

        >>> from pytz import timezone
        >>> utc = timezone('UTC')