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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 list_branch(self, repo_name):
 """ Lists the active Branch objects on a Repo. Params: * repo_name: The name of the repo. """

        req = proto.ListBranchRequest(repo=proto.Repo(name=repo_name))
        res = self.stub.ListBranch(req, metadata=self.metadata)
        if hasattr(res, 'branch_info'):
            return res.branch_info
        return []