tzinfo.py 文件源码

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')
        >>> eastern = timezone('US/Eastern')
        >>> fmt = '%Y-%m-%d %H:%M:%S %Z (%z)'

        We next create a datetime right on an end-of-DST transition point,
        the instant when the wallclocks are wound back one hour.

        >>> utc_dt = datetime(2002, 10, 27, 6, 0, 0, tzinfo=utc)
        >>> loc_dt = utc_dt.astimezone(eastern)
        >>> loc_dt.strftime(fmt)
        '2002-10-27 01:00:00 EST (-0500)'

        Now, if we subtract a few minutes from it, note that the timezone
        information has not changed.

        >>> before = loc_dt - timedelta(minutes=10)
        >>> before.strftime(fmt)
        '2002-10-27 00:50:00 EST (-0500)'

        But we can fix that by calling the normalize method

        >>> before = eastern.normalize(before)
        >>> before.strftime(fmt)
        '2002-10-27 01:50:00 EDT (-0400)'
        '''
        if dt.tzinfo is None:
            raise ValueError, 'Naive time - no tzinfo set'

        # Convert dt in localtime to UTC
        offset = dt.tzinfo._utcoffset
        dt = dt.replace(tzinfo=None)
        dt = dt - offset
        # convert it back, and return it
        return self.fromutc(dt)