code: def build_permuted_index(
              self,
              lshash,
              buckets,
              num_permutation,
              beam_size,
              num_neighbour):
          
          # Init a PermutedIndex
          pi = PermutedIndex(
              lshash,
              buckets,
              num_permutation,
              beam_size,
              num_neighbour)
          # get hash_name
          hash_name = lshash.hash_name
          self.permutedIndexs[hash_name] = pi
docs: Build a permutedIndex and store it into the dict self.permutedIndexs.
          lshash: the binary lshash object (nearpy.hashes.lshash).
          buckets: the buckets object corresponding to lshash. It's a dict object 
                   which can get from nearpy.storage.buckets[lshash.hash_name]
          num_permutation: the number of sorted randomly-permuted bucket key lists (SRPBKL).
          beam_size: beam size, details please refer to __init__() in nearpy.hashes.permutation.PermutedIndex 
          num_neighbour: the number of neighbour bucket keys needed to return in self.get_neighbour_keys().