函数使用 reduce, map, filter, compose

本是古典何须时尚 2024-04-18 16:43 68阅读 0赞

## reduce 用法 ##

reduce(func, seq) 等同于func(func(seq\[0\], seq\[1\]),seq\[2\]),…

from functools import reduce
    reduce(lambda x, y: x+y, [1,2,3,4,5]) # 使用 lambda 匿名函数15

## map 用法 ##

map(func, seq) 对序列中的每个元素应用func

from functools import reduce
    list(map(lambda x: x*2, [1,2,3,4,5]))

[2, 4, 6, 8, 10]

## filter 用法 ##

filter(func, seq) 返回函数为真的元素的列表

#from functools import filter
    list(filter(lambda x: x >2, [1,2,3,4,5]))

[3, 4, 5]

## compose 多层函数套用 ##

参考链接： https://mathieularose.com/function-composition-in-python/

### 使用1， 习惯函数套用 ###

def compose2(f, g):
        return lambda x: f(g(x))
    def double(x):
        return x * 2
    def inc(x):
        return x + 1
    def dec(x):
        return x-1
    inc_and_double = compose2(double, inc)
    print(inc_and_double(10)) #22
    inc_double_and_dec = compose2(compose2(dec, double), inc)
    print(inc_double_and_dec(10)) #21

22
    21

### 使用2 ###

import functools
    def compose(*functions):
        def compose2(f, g):
            return lambda x: f(g(x))
        return functools.reduce(compose2, functions, lambda x: x)
    inc_double_and_dec = compose(dec, double, inc)
    print(inc_double_and_dec(10))  #21

### 使用3 ###

import functools
    def compose(*functions):
        return functools.reduce(lambda f, g: lambda x: f(g(x)), functions, lambda x: x)
    inc_double_and_dec = compose(dec, double, inc)
    print(inc_double_and_dec(10))  #21

### 使用4 ###

def compose(*funcs):
        """Compose arbitrarily many functions, evaluated left to right. Reference: https://mathieularose.com/function-composition-in-python/ """
        # return lambda x: reduce(lambda v, f: f(v), funcs, x)
        if funcs:
            return reduce(lambda f, g: lambda *a, **kw: g(f(*a, **kw)), funcs)
        else:
            raise ValueError('Composition of empty sequence not supported.')
    def incXY(*args,**kwargs):
        sum_a = 0
        for i in args:
            sum_a += i
        for i, j in kwargs.items():
            sum_a +=j
        return sum_a
    def decXY(*args,**kwargs):
        sum_a = 0
        for i in args:
            sum_a += i
        for i, j in kwargs.items():
            sum_a -=j
        return sum_a
    XY_inc_dec = compose(incXY,decXY)
    print(XY_inc_dec(10,11,pintput=5))