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

        ln = self.online_branches if branches is None else branches
        for i, l in enumerate(ln):
            l._i = start + i