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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 downstream(self, node):
 """ Returns a list of all nodes this node has edges towards. Args: node (str):
 The node whose downstream nodes you want to find. Returns: list: A list of nodes that are immediately downstream from the node. """

        graph = self.graph
        if node not in graph:
            raise KeyError('node %s is not in graph' % node)
        return list(graph[node])