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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 _merge_groups(self, backends_list):
 """ merge a list backends_groups"""

        ret = {}
        for backends in backends_list:
            for b in backends:
                if b not in ret:
                    ret[b] = set([])
                for group in backends[b]:
                    ret[b].add(group)
        for b in ret:
            ret[b] = list(ret[b])
            ret[b].sort()
        return ret