# 30段极简Python代码：这些小技巧你都Get了么

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) # False
all_unique(y) # True

2. 字符元素组成判定

'''

'''
from collections import Counter

def 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('') # 4
byte_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 ceil

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

11. 逗号连接

'''

'''

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

12. 元音统计

'''

'''
import re

def count_vowels(str):
return len(len(re.findall(r'[aeiou]', str, re.IGNORECASE)))

count_vowels('foobar') # 3
count_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

'''

'''
ret = []
for i in arg:
if isinstance(i, list):
ret.extend(i)
else:
ret.append(i)
return ret

def deep_flatten(lst):
result = []
result.extend(
spread(list(map(lambda x: deep_flatten(x) if type(x) == list else x, lst))))
return result

deep_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 floor
difference_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

'''

'''
return a + b

def subtract(a, b):
return a - b

a, b = 4, 5
print((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) # True
has_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 b
return c

a = { '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 time

start_time = time.time()

a = 1
b = 2
c = a + b
print(c) #3

end_time = time.time()
total_time = end_time - start_time
print("Time: ", total_time)

# ('Time: ', 1.1205673217773438e-05)  

23.Try else

try:
2*3
except 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 operator
action = {
"-": operator.sub,
"/": operator.truediv,
"*": operator.mul,
"**": pow
}
print(action['-'](50, 25)) # 25

27.Shuffle

'''

'''
from copy import deepcopy
from random import randint

def 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_lst

foo = [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 ret

spread([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, a

a, b = -1, 14
swap(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

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