python - Python 中字典列表的条件操作

Question

我想根据另一个键的条件(例如 Gender == 'male')对这个字典列表中所有人的年龄求和:

list_of_dicts= [  
              {"Name": "Ethan", "Gender": "male", "Age": 11},
              {"Name": "Nathan", "Gender": "male", "Age": 6},
              {"Name": "Sophie", "Gender": "female", "Age": 14},
              {"Name": "Patrick", "Gender": "male", "Age": 11}
]

下面的代码完成了它，但我想知道是否有更 Pythonic/compact 的方法来做到这一点？也许像字典列表的 SQL 查询？

total_male_age = 0

for dict in list_of_dicts: 
    if dict.get("Gender") == "male":
        total_male_age = total_male_age + dict.get("Age")  


#total_male_age  = 28

Answer 1

这个怎么样？

>>> sum(d['Age'] for d in list_of_dicts if d['Gender'] == 'male')
28

从技术上讲，您在此处对生成器表达式调用 sum - 过滤到 Gender 等于“male”的字典。

PEP 289提供了一些进一步阅读的示例。

要查找乘积而不是总和:

import numpy as np
np.product([d['Age'] for d in list_of_dicts if d['Gender'] == 'male'])

如果您想在 Python 的标准库中查找产品:

from functools import reduce
from operator import mul
reduce(mul, (d['Age'] for d in list_of_dicts if d['Gender'] == 'male'), 1)