Usage of lambda/filter/map/reduce in python3 function

These functions of lambda/filter/map/reduce will definitely be used in interviews. This article mainly introduces the usage of these functions.

1.lambda

Anonymous function, the usage is as follows:

# lambada 参数,参数,参数 : 返回的表达式　

Example 1:

f = lambda x, y: x * y
print(f(2, 3))    # 6

Example 2:　

r = (lambda x, y: x+y)(1, 2)
print(r)          # 3

2 filter

filter(function, sequence): sequentially execute function(item) on the items in the sequence, and return the items whose execution result is True to form a filter object (iterable) (depending on the type of sequence).

Example:

def gt_5(x):
    return x > 5

r = filter(gt_5, range(10))
print(list(r))      # [6, 7, 8, 9]

3 map

map(function, sequence): execute function(item) in sequence on the items in the sequence, see the execution result to form a map object (iterable) and return.

Example:

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

r = map(mysum, range(5), range(5, 10))
print(list(r))      # [5, 7, 9, 11, 13]

4 reduce

In python3, reduce has been removed from the global namespace and needs to be imported from functiontools.

reduce(function, sequence, starting_value): Call the function iteratively on the items in the sequence. If there is starting_value, it can also be used as the initial value.

Example:

'''
遇到问题没人解答？小编创建了一个Python学习交流QQ群：531509025
寻找有志同道合的小伙伴，互帮互助,群里还有不错的视频学习教程和PDF电子书！
'''
def mysum(x, y):
    return x + y

from functools import reduce
r = reduce(mysum, range(10))
print(r)     # 45

5 Combined use

Example: Calculate 1! +2! +...+10!

def factorial(n):
    if n == 1:
        return 1
    return n*factorial(n-1)
r = reduce(lambda x, y: x + y, map(factorial, range(1, 11)))
print(r)    # 4037913

This is how a few functions are used. Isn't it simple?