code: def allele_clusters(dists, t=0.025):
      
      clusters = fcluster(linkage(dists), 0.025, criterion='distance')
      cluster_idx = defaultdict(list)
      for idx, cl in enumerate(clusters):
          cluster_idx[cl].append(idx)
      return cluster_idx
docs: Flat clusters from distance matrix
  
      Args:
          dists (numpy.array): pdist distance matrix
          t (float): fcluster (tree cutting) distance threshold
  
      Returns:
          dict of lists: cluster number to list of indices of distances in cluster