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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 node_from_nid(self, nid):
 """Return the node in the `Flow` with the given `nid` identifier"""

        for node in self.iflat_nodes():
            if node.node_id == nid: return node
        raise ValueError("Cannot find node with node id: %s" % nid)