code: def weighted_mean(items):
      a, b = zip(*items)
      return sum(a) / sum(b)
  
imports: import math
  from collections.abc import Iterable
  import numpy
  import sacrebleu
  import sklearn.metrics
  import random
  from collections import defaultdict
label_desc: Use image node_id 14 for calling a global function with example usage: weighted_mean(items) and returns: unknown