來源 : 機器之心

本文對 Python 中的函數(shù)式編程技術進行了簡單的入門介紹。

def?foo():
???print("foo")

bar?=?foo
bar()
#will?print?"foo"?to?the?console

class?Greeter:
???def?__init__(self,?greeting):
??????self.greeting?=?greeting
???def?__call__(self,?name):
??????return?self.greeting?+?"?"?+?name

morning?=?Greeter("good?morning")?#creates?the?callable?object
morning("john")?#?calling?the?object
#prints?"good?morning?john"?to?the?console

callable(morning)?#true
callable(145)?#false.?int?is?not?callable.?

#?store?in?dictionary
mapping?=?{
???0?:?foo,
???1?:?bar
}
x?=?input()?#get?integer?value?from?user
mapping[x]()?#call?the?func?returned?by?dictionary?access

「高階函數(shù)允許我們對動作執(zhí)行抽象，而不只是抽象數(shù)值。」

def?iterate(list_of_items):
????for?item?in?list_of_items:
????????print(item)

看起來很酷吧，但這只不過是一級抽象而已。如果我們想在對列表執(zhí)行迭代時進行打印以外的其他操作要怎么做呢？

def?iterate_custom(list_of_items,?custom_func):
???for?item?in?list_of_items:
????????custom_func(item)

def?add(x,?y):
????return?x?+?y
def?sub(x,?y):
????return?x?-?y
def?mult(x,?y):
????return?x?*?y
def?calculator(opcode):
????if?opcode?==?1:
???????return?add
????elif?opcode?==?2:
???????return?sub
????else:
???????return?mult?
my_calc?=?calculator(2)?#my?calc?is?a?subtractor
my_calc(5,?4)?#returns?5?-?4?=?1?
my_calc?=?calculator(9)?#my?calc?is?now?a?multiplier
my_calc(5,?4)?#returns?5?x?4?=?20.?

嵌套函數(shù)

def?fib(n):
????def?fib_helper(fk1,?fk,?k):
????????if?n?==?k:
???????????return?fk
????????else:
???????????return?fib_helper(fk,?fk1+fk,?k+1)
????if?n?<=?1:
???????return?n
????else:
???????return?fib_helper(0,?1,?1)

將該計算從函數(shù)主體移到函數(shù)參數(shù)，這具備非常強大的力量。因為它減少了遞歸方法中可能出現(xiàn)的冗余計算。

mult?=?lambda?x,?y:?x?*?y
mult(1,?2)?#returns?2

該 mult 函數(shù)的行為與使用傳統(tǒng) def 關鍵字定義函數(shù)的行為相同。

(lambda?x,?y:?x?*?y)(9,?10)?#returns?90

import?collections
pre_fill?=?collections.defaultdict(lambda:?(0,?0))
#all?dictionary?keys?and?values?are?set?to?0

def?multiply_by_four(x):
????return?x?*?4
scores?=?[3,?6,?8,?3,?5,?7]
modified_scores?=?list(map(multiply_by_four,?scores))
#modified?scores?is?now?[12,?24,?32,?12,?20,?28]

在 Python 3 中，map 函數(shù)返回的 map 對象可被類型轉(zhuǎn)換為 list，以方便使用。現(xiàn)在，我們無需顯式地定義 multiply_by_four 函數(shù)，而是定義 lambda 表達式：

modified_scores?=?list(map(lambda?x:?4?*?x,?scores))

even_scores?=?list(filter(lambda?x:?True?if?(x?%?2?==?0)?else?False,?scores))
#even_scores?=?[6,?8]

sum_scores?=?reduce((lambda?x,?y:?x?+?y),?scores)
#sum_scores?=?32

• Best Practices for Using Functional Programming in Python：https://kite.com/blog/python/functional-programming/

• Functional Programming Tutorials and Notes：https://www.hackerearth.com/zh/practice/python/functional-programming/functional-programming-1/tutorial/

原文鏈接：https://medium.com/better-programming/introduction-to-functional-programming-in-python-3d26cd9cbfd7