'Calculates the daylight savings offset according to the datetime.tzinfo spec'

def dst(self, dt):

    if (dt is None):
        return
    winInfo = self.getWinInfo(dt.year)
    if ((not self.fixedStandardTime) and self._inDaylightSavings(dt)):
        result = winInfo.daylight_bias
    else:
        result = winInfo.standard_bias
    return result
