变量,id()

 1 >>> a = 1
 2 >>> print id(a)
 3 2870961640
 4 >>> b = a
 5 >>> print id(b)
 6 2870961640
 7 >>> c = 1
 8 >>> print id(c)
 9 2870961640
10 >>>

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。

 1 # True
 2 a = 1
 3 b = 1
 4 print(a is b)
 5 
 6 # True
 7 a = "good"
 8 b = "good"
 9 print(a is b)
10 
11 # False
12 a = "very good morning"
13 b = "very good morning"
14 print(a is b)
15 
16 # False
17 a = []
18 b = []
19 print(a is b)