code: def trim_N_nucleotides(prefix, suffix):
      
      if 'N' in prefix:
          # trim prefix to exclude all occurrences of N
          rightmost_index = prefix.rfind('N')
          logger.debug(
              "Trimming %d nucleotides from read prefix '%s'",
              rightmost_index + 1, prefix)
          prefix = prefix[rightmost_index + 1:]
  
      if 'N' in suffix:
          leftmost_index = suffix.find('N')
          logger.debug(
              "Trimming %d nucleotides from read suffix '%s'",
              len(suffix) - leftmost_index,
              suffix)
          suffix = suffix[:leftmost_index]
  
      return prefix, suffix
docs: Drop all occurrences of 'N' from prefix and suffix nucleotide strings
      by trimming.