1"""
2Author: wangy325
3Date: 2024-07-22 16:57:01
4Description: 4个重要的函数
5"""
6
7from functools import reduce
8
9# ############### #
10# filter() #
11# map() #
12# reduce() #
13# zip() #
14# ############### #
15
16# Tips: 在命令行界面使用help()可以查看内置函数的帮助文档
17# filter()函数
18'''
19class filter(object)
20 | filter(function or None, iterable) --> filter object
21 |
22 | Return an iterator yielding those items of iterable for which function(item)
23 | is true. If function is None, return the items that are true
24'''
25
26l1 = [1, 2, 3, 4]
27f = filter(lambda x: x > 2, l1)
28print(type(f)) # <class 'filter'>
29
30for e in f:
31 print(e, end=', ')
32print()
33
34for p in filter(lambda e: e.startswith('a'),
35 ['apple', 'ass', 'pine', 'cindy', 'ark']):
36 print(p, end=', ')
37print()
38
39# map()函数
40# 将2个容器里的元素一一对应运算,
41# 直到少的那个容器所有元素都参与运算
42# 这个*map*不是k-v映射哦
43'''
44class map(object)
45 | map(func, *iterables) --> map object
46 |
47 | Make an iterator that computes the function using arguments from
48 | each of the iterables. Stops when the shortest iterable is exhausted.
49'''
50m = [2, 3, 4, 5, 6]
51mm = map(lambda x, y: x + y, l1, m)
52print(type(mm)) # <class 'map'>
53for e in mm:
54 print(e, end=", ")
55print()
56
57# zip()函数
58# 返回一个元组集
59# 元素的数量取决于实参列表中元素最短长度
60# 元组中元素的个数取决于实参的数量
61'''
62class zip(object)
63 | zip(*iterables, strict=False) --> Yield tuples until an input is exhausted.
64 |
65 | >>> list(zip('abcdefg', range(3), range(4)))
66 | [('a', 0, 0), ('b', 1, 1), ('c', 2, 2)]
67 |
68 | The zip object yields n-length tuples, where n is the number of iterables
69 | passed as positional arguments to zip(). The i-th element in every tuple
70 | comes from the i-th iterable argument to zip(). This continues until the
71 | shortest argument is exhausted.
72 |
73 | If strict is true and one of the arguments is exhausted before the others,
74 | raise a ValueError.
75'''
76d = dict(zip('abc', ['va', 'vb', 'vc']))
77for k, v in d.items():
78 print(f'{k}: {v}')
79
80lz = list(zip('abcdefg', range(5), range(4)))
81for t in lz:
82 print(t, end=", ")
83print()
84
85# reduce()函数
86# 对可迭代参数的所有元素依次运算
87# 返回运算后的值
88# 可选一个初始值作为运算参数
89'''
90reduce(...)
91 reduce(function, iterable[, initial]) -> value
92
93 Apply a function of two arguments cumulatively to the items of a sequence
94 or iterable, from left to right, so as to reduce the iterable to a single
95 value. For example, reduce(lambda x, y: x+y, [1, 2, 3, 4, 5]) calculates
96 ((((1+2)+3)+4)+5). If initial is present, it is placed before the items
97 of the iterable in the calculation, and serves as a default when the
98 iterable is empty.
99'''
100
101val = reduce(lambda x, y: x + y, ['p', 'p', 'l', 'e'], 'a')
102print(val) # apple
简体中文
