code: def calculate_weighted_avg(bonds):
      
      minimum_bond = min(bonds)
      weighted_sum = 0.0
      total_sum = 0.0
      for entry in bonds:
          weighted_sum += entry * exp(1 - (entry / minimum_bond) ** 6)
          total_sum += exp(1 - (entry / minimum_bond) ** 6)
      return weighted_sum / total_sum
docs: Returns the weighted average bond length given by
      Hoppe's effective coordination number formula.
  
      Args:
          bonds (list): list of floats that are the
          bond distances between a cation and its
          peripheral ions