code: def group_unique_sequences(
          allele_reads,
          max_prefix_size=None,
          max_suffix_size=None):
      
      groups = defaultdict(set)
      for r in allele_reads:
          prefix = r.prefix
          allele = r.allele
          suffix = r.suffix
          if max_prefix_size and len(prefix) > max_prefix_size:
              prefix = prefix[-max_prefix_size:]
          if max_suffix_size and len(suffix) > max_suffix_size:
              suffix = suffix[:max_suffix_size]
          key = (prefix, allele, suffix)
          groups[key].add(r)
      return groups
docs: Given a list of AlleleRead objects, extracts all unique
      (prefix, allele, suffix) sequences and associate each with a list
      of reads that contained that sequence.