enumerate 替代 range(len(x))

data = [1, 2, 3, 5]

# BAD:
for i in range(len(data)):
    if data[i] < 3:
        data[i] = 0
        
print(data)

# GOOD:
for idx, num in enumerate(data):
    if num < 3:
        data[idx] = 0
        
print(data) 

##########  output  ##########
[0, 0, 3, 5]
[0, 0, 3, 5]

列表表达式替代循环语句

# BAD:
squares = []
for i in range(10):
    squares.append(i*i)  
    
print(squares)    

# GOOD:
squares = [i*i for i in range(10)]
print(squares) 

##########  output  ##########
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

使用 sorted() 对复杂对象排序

# data = [1, 3, 4, 5, -1]
data = (1, 3, 4, 5, -1)
sorted_data = sorted(data, reverse=True)

print(sorted_data)

data = [{'name':'Jack', 'age':6},
        {'name':'Rose', 'age':5},
        {'name':'Jia', 'age':16}]

sorted_data = sorted(data, key=lambda x: x['age'] )
print(sorted_data)

##########  output  ##########
[5, 4, 3, 1, -1]
[{'name': 'Rose', 'age': 5}, {'name': 'Jack', 'age': 6}, {'name': 'Jia', 'age': 16}]

使用 sets() 保存唯一值

my_list = [1,3,4,5,6,6,7,7,7,7]
my_set = set(my_list)
print(my_set)

print({3,4,5,6,6,8,2,4,5,5})

##########  output  ##########
{1, 3, 4, 5, 6, 7}
{2, 3, 4, 5, 6, 8}

使用迭代器节省内存

import sys

my_list = [i for i in range(1000)]
print(sum(my_list))
print(sys.getsizeof(my_list), 'bytes')

my_gen = (i for i in range(1000))
print(sum(my_gen))
print(sys.getsizeof(my_gen), 'bytes')

##########  output  ##########
499500
9016 bytes
499500
112 bytes

使用 .get() 和 .setdefault() 设置字典返回默认值

my_dict = {'item':'football', 'price':100}
count = my_dict.get('count', 0)
print(count)

count = my_dict.setdefault('count', 0)
print(count)
print(my_dict)

##########  output  ##########
0
0
{'item': 'football', 'price': 100, 'count': 0}##

使用 collection.Counter 统计字典元素数量

from collections import Counter

my_list = [1,2,3,5,6,6,3,5,6,6,6]
counter = Counter(my_list)
print(counter)
print(counter[2])
print(counter.most_common(2))

##########  output  ##########
Counter({6: 5, 3: 2, 5: 2, 1: 1, 2: 1})
1
[(6, 5), (3, 2)]

使用 f-string 输出字符串**(python3.6+)**

name = 'Alex'
print(f'hello {name}')

i = 10
print(f'{i} squared is {i*i}')

##########  output  ##########
hello Alex
10 squared is 100

使用 .join()连接分割字符串

list_of_string = ['Hello','my','world','!']

# BAD:
my_string = ''
for i in list_of_string:
    my_string += i + ' '
print(my_string)    

# GOOD:
my_string = ' '.join(list_of_string)
print(my_string)

##########  output  ##########
Hello my world ! 
Hello my world !

使用 {**d1,**d2} 合并字典元素（Python3.5+）

d1 = {'item':'football', 'price':100}
d2 = {'item':'football', 'count':10}
merge_dict = {**d1, **d2}
print(merge_dict)

##########  output  ##########
{'item': 'football', 'price': 100, 'count': 10}

使用 if x in [abc] 简化元素查询

colors = ['blue', 'green', 'red']

c = 'red'
if c in colors:
    print(f'{c} is main color.')
    
##########  output  ##########
red is main color.