# 30段超实用Python代码

 导读 许多人在数据科学、机器学习、web开发、脚本编写和自动化等领域中都会使用Python，它是一种十分流行的语言。

Python流行的部分原因在于简单易学。

1. 唯一性

```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. 变位词(相同字母异序词)

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

3. 内存

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

4. 字节大小

```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. 首字母大写

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

7. 列表细分

```def chunk(list, size):
return [list[i:i+size] for i in range(0,len(list), size)]```

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. 计数

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

10. 链式比较

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

11. 逗号分隔

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

12. 元音计数

```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

```def spread(arg):
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. 寻找差异

```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. 输出差异

```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

```def add(a, b):
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. 重复值存在与否

```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. 合并字库

```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. 将两个列表转换为字库

```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. 列举

```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. 时间成本

```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语句

```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. 出现频率很高的元素

```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(正反读有一样的字符串)

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

26. 不用if-else语句的计算器

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

27. 随机排序

```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

29. 交换变量

```def swap(a, b):
return b, a
a, b = -1, 14
swap(a, b) # (14, -1)```

30. 获取丢失部分的默认值

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

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