code: def sub_working_days(self, day, delta,
                           extra_working_days=None, extra_holidays=None,
                           keep_datetime=False):
          
          delta = abs(delta)
          return self.add_working_days(
              day, -delta,
              extra_working_days, extra_holidays, keep_datetime=keep_datetime)
docs: Substract `delta` working days to the date.
  
          This method is a shortcut / helper. Users may want to use either::
  
              cal.add_working_days(my_date, -7)
              cal.sub_working_days(my_date, 7)
  
          The other parameters are to be used exactly as in the
          ``add_working_days`` method.
  
          A negative ``delta`` argument will be converted into its absolute
          value. Hence, the two following calls are equivalent::
  
              cal.sub_working_days(my_date, -7)
              cal.sub_working_days(my_date, 7)
  
          As in ``add_working_days()`` you can set the parameter
          ``keep_datetime`` to ``True`` to make sure that if your ``day``
          argument is a ``datetime``, the returned date will also be a
          ``datetime`` object.