>>> number
[1, 2, 3, 4, 5]
>>> number2 = []
>>> for i in number:
... i = i+2
... number2.append(i)
...
>>> number2
[3, 4, 5, 6, 7]
如果用上面的增强赋值，i = i+2可以写成 i +=2，试一试吧：
>>> number
[1, 2, 3, 4, 5]
>>> number2 = []
>>> for i in number:
... i +=2
... number2.append(i)
...
>>> number2
[3, 4, 5, 6, 7]
这就是增强赋值。为什么用增强赋值？因为i +=2，比i = i+2计算更快，后者右边还要拷贝一个i。
上面的例子还能修改，别忘记了list解析的强大功能呀。
>>> [i+2 for i in number]
[3, 4, 5, 6, 7]
