code: def mask_umi(umi, umi_quals, quality_encoding,  quality_filter_threshold):
      ''' Mask all positions where quals < threshold with "N" '''
      below_threshold = get_below_threshold(
          umi_quals, quality_encoding, quality_filter_threshold)
      new_umi = ""
  
      for base, test in zip(umi, below_threshold):
          if test:
              new_umi += "N"
          else:
              new_umi += base
  
      return new_umf mask_umi(umi, umi_quals, quality_encoding,  quality_filter_threshold):
      ''' Mask all positions where quals < threshold with "N" '''
      below_threshold = get_below_threshold(
          umi_quals, quality_encoding, quality_filter_threshold)
      new_umi = ""
  
      for base, test in zip(umi, below_threshold):
          if test:
              new_umi += "N"
          else:
              new_umi += base
  
      return new_umi
docs: Mask all positions where quals < threshold with "N"