Returns a dictionary with the variables that must be added to the
        input file in order to connect this :class:`Node` to its dependencies.

def connecting_vars(self):
        """
        Returns a dictionary with the variables that must be added to the
        input file in order to connect this :class:`Node` to its dependencies.
        """
        vars = {}
        for prod in self.products:
            vars.update(prod.connecting_vars())

        return vars