变量,id()

 >>> a = 1
 >>> print id(a)
 2870961640
 >>> b = a
 >>> print id(b)
 2870961640
 >>> c = 1
 >>> print id(c)
 2870961640
 >>>

在Python中，整数和短小的字符，Python都会缓存这些对象，以便重复使用。当我们创建多个等于1的引用时，实际上是让所有这些引用指向同一个对象。

 # True
 a = 1
 b = 1
 print(a is b)

 # True
 a = "good"
 b = "good"
 print(a is b)

 # False
 a = "very good morning"
 b = "very good morning"
 print(a is b)

 # False
 a = []
 b = []
 print(a is b)