Python 2 和 Python 3 中的 for 有一点不一样

# Python2
>>> i = 1                       
>>> a = [i for i in range(4)]   
>>> i                           
3                               

# Python3
>>> i = 1                      
>>> a = [i for i in range(4)]  
>>> i                          
1                              

Python 2 中的 for 循环会污染全局变量，Python 3 不会。这个问题只会出现在列表推导式中，对于普通的 for 循环，i 的值都是变的。对于集合推导式，i 的值不会变

# Python3
>>> i = 2                         
>>> a = {i for i in range(32)}    
>>> a                             
{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
, 24, 25, 26, 27, 28, 29, 30, 31} 
>>> i                             
2        

# Python 2 和 Python 3 一样的结果
# Python2 
>>> i = 3
>>> a = {i for i in range(6)}
>>> i
3                       

>>> i = 3             
>>> for i in range(5):
...     print(i)      
...                   
0                     
1                     
2                     
3                     
4                     
>>> i                 
4