code: def reset_obscov(self,arg=None):
          
          self.logger.statement("resetting obscov")
          self.__obscov = None
          if arg is not None:
              self.obscov_arg = arg
docs: reset the obscov attribute to None
  
          Parameters
          ----------
          arg : str or pyemu.Matrix
              the value to assign to the obscov attribute.  If None,
              the private __obscov attribute is cleared but not reset