Warning at the same labeled components

[eliftu]

Labels need to be unique. it will leads failure, when there is the same labeled components. Check when adding.

[p-snft]

I think something like this would solve the problem:

class EnergySystem:
    (...)
    def add(self, *nodes):
        """Add :class:`nodes <oemof.network.Node>` to this energy system."""
        new_nodes = {node.label: node for node in nodes}
        if self._nodes.keys().isdisjoint(new_nodes.keys()):
            self._nodes.update(new_nodes)
        else:
            common_labels = self._nodes.keys() & new_nodes.keys()
            raise ValueError(f"EnergySystem already contains Node(s) labeled {common_labels}.")
        for n in nodes:
            self.signals[type(self).add].send(n, EnergySystem=self)