Question

function = ({"Books":10,"pens":20},[("Books",-5),("pens",-11),("pencils",3)])

目标：更新字典以输出：{“图书”：5，“笔”：9，“铅笔”：3}

for key,value in dicto.items():
        for item in mylist:
            if key == item[0]:
                dict[key] += item[1]

为什么我的输出不包括铅笔键？

Answer 1

您正在迭代原始字典中的键，因此key永远不会等于铅笔。您应该迭代遍历列表中给出的键

>>> def f(D, L):
...     for k, v in L:
...         D[k] = D.get(k, 0) + v
...     return D
... 
>>> f({"Books":10,"pens":20},[("Books",-5),("pens",-11),("pencils",3)])
{'pencils': 3, 'Books': 5, 'pens': 9}

除了：

Counter类适用于此类事物

>>> from collections import Counter
>>> def f(D, L):
...     return Counter(D) + Counter(dict(L))
... 
>>> f({"Books":10,"pens":20},[("Books",-5),("pens",-11),("pencils",3)])
Counter({'pens': 9, 'Books': 5, 'pencils': 3})

Answer 2

for key, value in mylist:
    dict[key] = dict.get(key, 0) + value

受AChampion的启发

使用从列表中添加其他值的函数更新字典

2 个答案: