快捷導(dǎo)航

Python中reduce()函數(shù)的用法詳細(xì)解讀

更新時(shí)間：2023年08月21日 09:50:52 作者：IT之一小佬

這篇文章主要介紹了Python中reduce()函數(shù)的用法詳細(xì)解讀,reduce函數(shù)是通過(guò)函數(shù)對(duì)迭代器對(duì)象中的元素進(jìn)行遍歷操作,但需要注意的是?reduce?函數(shù)返回的是計(jì)算的結(jié)果,而?map/filter?返回的是作用后的迭代器對(duì)象,需要的朋友可以參考下

Python中的reduce()函數(shù)

reduce()源碼：

def reduce(function, sequence, initial=None): # real signature unknown; restored from __doc__
    """
    reduce(function, sequence[, initial]) -> value
    Apply a function of two arguments cumulatively to the items of a sequence,
    from left to right, so as to reduce the sequence to a single value.
    For example, reduce(lambda x, y: x+y, [1, 2, 3, 4, 5]) calculates
    ((((1+2)+3)+4)+5).  If initial is present, it is placed before the items
    of the sequence in the calculation, and serves as a default when the
    sequence is empty.
    """
    pass

從上述可以看到，reduce()有三個(gè)參數(shù)，第一個(gè)是函數(shù)function，第二個(gè)是序列sequence，第三個(gè)是initial，為初始值，默認(rèn)為None

reduce(func，lst)，其中func必須至少有兩個(gè)參數(shù)。每次func計(jì)算的結(jié)果繼續(xù)和序列的下?個(gè)元素做累積計(jì)算。

注意：reduce()傳?的參數(shù)func必須至少接收2個(gè)參數(shù)。

需求：計(jì)算 list1 序列中各個(gè)數(shù)字的累加和。

示例代碼1：

import functools
list1 = [1, 2, 3, 4, 5]
#  方法一
def func(a, b):
    return a + b
result = functools.reduce(func, list1)
print(result)  # 15
# 方法二
result2 = functools.reduce(lambda x, y: x + y, list1)
print(result2)

運(yùn)行結(jié)果：

示例代碼2：

import functools
list1 = [1, 2, 3, 4, 5]
#  方法一
def func(a, b):
    return a * b
result = functools.reduce(func, list1)
print(result)  # 15
# 方法二
result2 = functools.reduce(lambda x, y: x * y, list1)
print(result2)

運(yùn)行結(jié)果：

示例代碼3：

import functools
list1 = [1, 2, 3, 4, 5]
list2 = [1, 1, 1, 1, 1]
list3 = [0, 0, 0, 0, 0]
list4 = [0, 0, 0, 0, 1]
result1 = functools.reduce(lambda x, y: x & y, list1)
result2 = functools.reduce(lambda x, y: x & y, list2)
result3 = functools.reduce(lambda x, y: x | y, list3)
result4 = functools.reduce(lambda x, y: x | y, list4)
print(result1)
print(result2)
print(result3)
print(result4)

運(yùn)行結(jié)果：

示例代碼4：

from functools import reduce
def add(x, y):
    return x + y
a = [1, 2, 3, 4, 5]
#  reduce()兩個(gè)參數(shù)
ret1 = reduce(add, a)
print(ret1)
#  reduce()三個(gè)參數(shù)
ret2 = reduce(add, a, 6)
print(ret2)

運(yùn)行結(jié)果：

示例代碼5：【mongo和es語(yǔ)句中使用reduce】

from functools import reduce
from mongoengine import Q
from mongoengine.queryset.visitor import Q
from elasticsearch_dsl import Q as EQ
# query_list = ['x', 'y', 'z']  # 字符串報(bào)錯(cuò)：TypeError: unsupported operand type(s) for &: 'str' and 'str'
# query_list = [2, 3]  # 2
# query_list = [2, 3, 4]  # 0
# mongo中使用
query_list = [Q(aa="aa"), Q(bb='bb'), Q(cc='cc'), Q(dd='dd')]  # (Q(**{'aa': 'aa'}) & Q(**{'bb': 'bb'}) & Q(**{'cc': 'cc'}) & Q(**{'dd': 'dd'}))
res = reduce(lambda x, y: x & y, query_list)
print(res)
# es中使用
query_list = [EQ(aa="aa"), EQ(bb='bb'), EQ(cc='cc'), EQ(dd='dd')]  # MatchAll(dd='dd')
res = reduce(lambda x, y: x & y, query_list)
print(res)

運(yùn)行結(jié)果：