reduce()函数

Posted 2021-07-17 小小菜_v

reduce()函数

reduce() 函数会对参数序列中元素进行累积。

函数将一个数据集合（链表，元组等）中的所有数据进行下列操作：用传给 reduce 中的函数 function（有两个参数）先对集合中的第 1、2 个元素进行操作，得到的结果再与第三个数据用 function 函数运算，最后得到一个结果。

"""
reduce 函数
"""
from functools import reduce


def add(x, y):
    return x + y


if __name__ == '__main__':
    list1 = [1, 2, 3]
    a = reduce(add, list1)
    print(a)

输出如下

C:\\Python_Practice\\venv\\Scripts\\python.exe C:/Python_Practice/reduce_demo.py
6

Process finished with exit code 0

但是如下情况则不一样

"""
reduce 函数
"""
from functools import reduce


def dict_add(x, y):
    return x["age"] + y["age"]


if __name__ == '__main__':
    list2 = [{"name": "Lily", "age": 11},
             {"name": "Bob", "age": 15},
             {"name": "Joe", "age": 18}]

    b = reduce(dict_add, list2)
    print(b)

输出报错

C:\\Python_Practice\\venv\\Scripts\\python.exe C:/Python_Practice/reduce_demo.py
Traceback (most recent call last):
  File "C:/Python_Practice/reduce_demo.py", line 23, in <module>
    b = reduce(dict_add, list2)
  File "C:/Python_Practice/reduce_demo.py", line 12, in dict_add
    return x["age"] + y["age"]
TypeError: 'int' object is not subscriptable

Process finished with exit code 1

由于x,y值是取list2列表中的第1，2个元素age的值，返回的是int型26赋值给下一轮的x,若再取x[“age”],则会报类型错误，所以得做如下处理，添加一个默认值：

"""
reduce 函数
"""
from functools import reduce


def add(x, y):
    return x + y


def dict_add(x, y):
    return x + y["age"]


if __name__ == '__main__':
    # list1 = [1, 2, 3]
    # a = reduce(add, list1)
    # print(a)
    list2 = [{"name": "Lily", "age": 11},
             {"name": "Bob", "age": 15},
             {"name": "Joe", "age": 18}]

    b = reduce(dict_add, list2, 0)
    print(b)

返回如下：

C:\\Python_Practice\\venv\\Scripts\\python.exe C:/Python_Practice/reduce_demo.py
44

Process finished with exit code 0