我该如何解决？

Question

print("Orignal missing: %d"% sum(miss_bool))
train.loc[miss_bool,"Item_Weight"] = train.loc[miss_bool,"Item_Identifier"].apply(lambda x: item_avg_weight[x])
print("Final missing: %d"% sum(train["Item_Weight"].isnull()))

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TypeError 追溯（最近一次通话）  在 ---->

      1 print("Orignal missing: %d"% sum(miss_bool))
      2 train.loc[miss_bool,"Item_Weight"] = train.loc[miss_bool,"Item_Identifier"].apply(lambda x: item_avg_weight[x])
      3 print("Final missing: %d"% sum(train["Item_Weight"].isnull()))

TypeError：“方法”对象不可迭代