code: def total_level(source_levels):
      
      sums = 0.0
      for l in source_levels:
          if l is None:
              continue
          if l == 0:
              continue
          sums += pow(10.0, float(l) / 10.0)
      level = 10.0 * math.log10(sums)
      return level
docs: Calculates the total sound pressure level based on multiple source levels