Adds the name and attribute of a dependent variable to the list 
        for plotting/tabulating functions.

def do_dep(self, args):
        """Adds the name and attribute of a dependent variable to the list 
        for plotting/tabulating functions."""
        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