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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 index_buses(self, buses=None, start=0):
 """ Updates the indices of all buses. @param start: Starting index, typically 0 or 1. @type start: int """

        bs = self.connected_buses if buses is None else buses
        for i, b in enumerate(bs):
            b._i = start + i