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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def add_bond(self, particle_pair):
 """Add a bond between two Particles. Parameters particle_pair : indexable object, length=2, dtype=mb.Compound The pair of Particles to add a bond between """

        if self.root.bond_graph is None:
            self.root.bond_graph = BondGraph()

        self.root.bond_graph.add_edge(particle_pair[0], particle_pair[1])