code: def do_dep(self, args):
          
          vals = args.split()
          twin = None
          if len(vals) > 1:
              if len(vals) == 2:
                  var, plot = vals
              elif len(vals) == 3:
                  var, plot, twin = vals
          else:
              var = vals[0]
              plot = None
  
          if not self._validate_var(var):
              msg.err("Variable {} is not a valid file name and property combination.".format(var))
          else:
              if var in self.curargs["dependents"]:
                  self.curargs["dependents"].remove(var)
              self.curargs["dependents"].append(var)
              if plot is not None:
                  self.curargs["plottypes"][var] = plot
              if twin is not None:
                  self.curargs["twinplots"][var] = twin
docs: Adds the name and attribute of a dependent variable to the list 
          for plotting/tabulating functions.