Apply the given offset/observance to a DatetimeIndex of dates.

        Parameters
        ----------
        dates : DatetimeIndex
            Dates to apply the given offset/observance rule

        Returns
        -------
        Dates with rules applied

def _apply_rule(self, dates):
        """
        Apply the given offset/observance to a DatetimeIndex of dates.

        Parameters
        ----------
        dates : DatetimeIndex
            Dates to apply the given offset/observance rule

        Returns
        -------
        Dates with rules applied
        """
        if self.observance is not None:
            return dates.map(lambda d: self.observance(d))

        if self.offset is not None:
            if not isinstance(self.offset, list):
                offsets = [self.offset]
            else:
                offsets = self.offset
            for offset in offsets:

                # if we are adding a non-vectorized value
                # ignore the PerformanceWarnings:
                with warnings.catch_warnings():
                    warnings.simplefilter("ignore", PerformanceWarning)
                    dates += offset
        return dates