code: def verify(self):
          
          if self.firstdate >= self.lastdate:
              raise ValueError(
                  f'Unplausible timegrid. The first given date '
                  f'{self.firstdate}, the second given date is {self.lastdate}.')
          if (self.lastdate-self.firstdate) % self.stepsize:
              raise ValueError(
                  f'Unplausible timegrid. The period span between the given '
                  f'dates {self.firstdate} and {self.lastdate} is not '
                  f'a multiple of the given step size {self.stepsize}.')
docs: Raise an |ValueError| if the dates or the step size of the time
          frame are inconsistent.