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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 flatten(self, condition=None, start=None):
 """ Iterate over the subgraph that is entirely reachable by condition starting from the given start node or the ObjectGraph root """

        if start is None:
            start = self
        start = self.getRawIdent(start)
        return self.graph.iterdata(start=start, condition=condition)