# 建议收藏！Python30段非常实用的技巧

Python 是机器学习最广泛采用的编程语言，它最重要的优势在于编程的易用性。如果读者对基本的 Python 语法已经有一些了解，那么这篇文章可能会给你一些启发。作者简单概览了 30 段代码，它们都是平常非常实用的技巧，我们只要花几分钟就能从头到尾浏览一遍。

1. 重复元素判定

def all_unique(lst):    return len(lst) == len(set(lst))x = [1,1,2,2,3,2,3,4,5,6]y = [1,2,3,4,5]all_unique(x) # Falseall_unique(y) # True

2. 字符元素组成判定

from collections import Counterdef anagram(first, second):return Counter(first) == Counter(second)anagram("abcd3", "3acdb") # True

3. 内存占用

import sys variable = 30 print(sys.getsizeof(variable)) # 24

4. 字节占用

def byte_size(string):return(len(string.encode('utf-8')))byte_size(':grinning:') # 4byte_size('Hello World') # 11

5. 打印 N 次字符串

n = 2; s ="Programming"; print(s * n);# ProgrammingProgramming

6. 大写第一个字母

s = "programming is awesome"print(s.title())# Programming Is Awesome

7. 分块

from math import ceildef chunk(lst, size):return list(        map(lambda x: lst[x * size:x * size + size],            list(range(0, ceil(len(lst) / size)))))chunk([1,2,3,4,5],2)# [[1,2],[3,4],5]

8. 压缩

def compact(lst):return list(filter(bool, lst))compact([0, 1, False, 2, '', 3, 'a', 's', 34])# [ 1, 2, 3, 'a', 's', 34 ]

9. 解包

array = [['a', 'b'], ['c', 'd'], ['e', 'f']]transposed = zip(*array)print(transposed)# [('a', 'c', 'e'), ('b', 'd', 'f')]

10. 链式对比

a = 3print( 2 < a < 8) # Trueprint(1 == a < 2) # False

11. 逗号连接

hobbies = ["basketball", "football", "swimming"]print("My hobbies are: " + ", ".join(hobbies))# My hobbies are: basketball, football, swimming

12. 元音统计

import redef count_vowels(str):return len(len(re.findall(r'[aeiou]', str, re.IGNORECASE)))count_vowels('foobar') # 3count_vowels('gym') # 0

13. 首字母小写

def decapitalize(string):return str[:1].lower() + str[1:]decapitalize('FooBar') # 'fooBar'decapitalize('FooBar') # 'fooBar'

14. 展开列表

def spread(arg):    ret = []for i in arg:if isinstance(i, list):            ret.extend(i)else:            ret.append(i)return retdef deep_flatten(lst):    result = []    result.extend(        spread(list(map(lambda x: deep_flatten(x) if type(x) == list else x, lst))))return resultdeep_flatten([1, [2], [[3], 4], 5]) # [1,2,3,4,5]

15. 列表的差

def difference(a, b):    set_a = set(a)    set_b = set(b)    comparison = set_a.difference(set_b)return list(comparison)difference([1,2,3], [1,2,4]) # [3]

16. 通过函数取差

def difference_by(a, b, fn):    b = set(map(fn, b))return [item for item in a if fn(item) not in b]from math import floordifference_by([2.1, 1.2], [2.3, 3.4],floor) # [1.2]difference_by([{ 'x': 2 }, { 'x': 1 }], [{ 'x': 1 }], lambda v : v['x'])# [ { x: 2 } ]

17. 链式函数调用

def add(a, b):return a + bdef subtract(a, b):return a - ba, b = 4, 5print((subtract if a > b else add)(a, b)) # 9

18. 检查重复项

def has_duplicates(lst):    return len(lst) != len(set(lst))x = [1,2,3,4,5,5]y = [1,2,3,4,5]has_duplicates(x) # Truehas_duplicates(y) # False

19. 合并两个字典

def merge_two_dicts(a, b):    c = a.copy()   # make a copy of a     c.update(b)    # modify keys and values of a with the ones from breturn ca = { 'x': 1, 'y': 2}b = { 'y': 3, 'z': 4}print(merge_two_dicts(a, b))# {'y': 3, 'x': 1, 'z': 4}

def merge_dictionaries(a, b)   return {**a, **b}a = { 'x': 1, 'y': 2}b = { 'y': 3, 'z': 4}print(merge_dictionaries(a, b))# {'y': 3, 'x': 1, 'z': 4}

20. 将两个列表转化为字典

def to_dictionary(keys, values):return dict(zip(keys, values))keys = ["a", "b", "c"]    values = [2, 3, 4]print(to_dictionary(keys, values))# {'a': 2, 'c': 4, 'b': 3}

21. 使用枚举

list = ["a", "b", "c", "d"]for index, element in enumerate(list): print("Value", element, "Index ", index, )# ('Value', 'a', 'Index ', 0)# ('Value', 'b', 'Index ', 1)#('Value', 'c', 'Index ', 2)# ('Value', 'd', 'Index ', 3)

22. 执行时间

import timestart_time = time.time()a = 1b = 2c = a + bprint(c) #3end_time = time.time()total_time = end_time - start_timeprint("Time: ", total_time)# ('Time: ', 1.1205673217773438e-05)

23.Try else

try:2*3except TypeError:    print("An exception was raised")else:    print("Thank God, no exceptions were raised.")#Thank God, no exceptions were raised.

24. 元素频率

def most_frequent(list):return max(set(list), key = list.count)list = [1,2,1,2,3,2,1,4,2]most_frequent(list)

25. 回文序列

def palindrome(string):from re import sub    s = sub('[\W_]', '', string.lower())return s == s[::-1]palindrome('taco cat') # True

26. 不使用 if-else 的计算子

import operatoraction = {"+": operator.add,"-": operator.sub,"/": operator.truediv,"*": operator.mul,"**": pow}print(action['-'](50, 25)) # 25

27.Shuffle

from copy import deepcopyfrom random import randintdef shuffle(lst):    temp_lst = deepcopy(lst)    m = len(temp_lst)while (m):        m -= 1        i = randint(0, m)        temp_lst[m], temp_lst[i] = temp_lst[i], temp_lst[m]return temp_lstfoo = [1,2,3]shuffle(foo) # [2,3,1] , foo = [1,2,3]

28. 展开列表

def spread(arg):    ret = []for i in arg:if isinstance(i, list):            ret.extend(i)else:            ret.append(i)return retspread([1,2,3,[4,5,6],[7],8,9]) # [1,2,3,4,5,6,7,8,9]

29. 交换值

def swap(a, b):return b, aa, b = -1, 14swap(a, b) # (14, -1)spread([1,2,3,[4,5,6],[7],8,9]) # [1,2,3,4,5,6,7,8,9]

30. 字典默认值

d = {'a': 1, 'b': 2}print(d.get('c', 3)) # 3