python 共享引用：多个变量引用同一对象

>>> x = 10
>>> y = 10
>>> x == y
True

>>> a = "tom"
>>> b = "tom"
>>> a == b
True

>>> x = 10
>>> y = 10
>>> x is y
True
>>> a = "tom"
>>> b = "tom"
>>> a is b
True

>>> x = 1000
>>> y = 1000
>>> x == y
True
>>> x is y
False

>>> peter = "www.baidu.com"
>>> queena = "www.baidu.com"
>>> peter is queena
False
>>> peter == queena
True

>>> id(x)
10251040
>>> id(y)
10251064
>>> id(peter)
140585861478696
>>> id(queena)
140585861478752