def rollback(self, dt):
        dt = as_timestamp(dt)
        if not self.onOffset(dt):
            dt = dt - self.__class__(1, normalize=self.normalize, **self.kwds)
        return dt
Roll provided date backward to next offset only if not on offset
dataset/ETHPy150Open pydata/pandas/pandas/tseries/offsets.py/DateOffset.rollback