2018-10-21 Python29 ==和is

• == 是用来判断值是否相等
• is 是判断是否指向了同一个东西

In [1]: a = [11,22,33]

In [2]: b = [11,22,33]

In [3]: a == b
Out[3]: True

In [4]: a is b
Out[4]: False

In [5]: id(a)
Out[5]: 139742505050824

In [6]: id(b)
Out[6]: 139742505051912



In [7]: c = a

In [8]: id(c)
Out[8]: 139742505050824

In [9]: c is a
Out[9]: True

In [10]: a==c
Out[10]: True

有一小部分数字存在了常量区，变量要引用这些值时，就都会指向存在常量区的这些值：[-5 , 256]

#正数
In [29]: a = 256

In [30]: b = 256

In [31]: a is b
Out[31]: True


In [35]: a = 257

In [36]: b = 257

In [37]: a is b
Out[37]: False


#负数
In [65]: a=-5

In [66]: b=-5

In [67]: a is b
Out[67]: True


In [71]: a=-6

In [72]: b=-6

In [73]: a is b
Out[73]: False