python is 和 ==的不同

is是俩个变量指向同一个对象的时候

==是俩个对象的值相同

>>> a = [1, 2, 3]
>>> b = a
>>> b is a 
True
>>> b == a
True
>>> b = a[:]
>>> b is a
False
>>> b == a
True

python的缓存只是支持小整型的运算

>>> 100 is 10**2
True
>>> 1000 is 10**3
False
>>> 1000 == 10**3
True

同样的规则适用于字符串

>>> "a" is "a"
True
>>> "aa" is "a" * 2
True
>>> x = "a"
>>> "aa" is x * 2
False
>>> "aa" is intern(x*2)
True

来源 ->>Stack Overflow
python源码学习 ->> intern