10 变量引用

a=1
print("a address is ",id(a))

b=a
c=b
print("b address is ",id(b))
print("c address is ",id(c))    

打印结果：
a address is  140706134913296      #b c a 都指向 1 所在的内存空间
b address is  140706134913296
c address is  140706134913296

b=2
print("b address is ",id(b))
print("c address is ",id(c))

打印结果：
b address is  140706134913328    #b  指向2所在的内存空间
c address is  140706134913296    #修改b后，c 仍然指向 1 所在的内存空间

a=3
print("c address is ",id(c))    
print("c=%d"%c)
打印结果：
c address is  140706134913296   #修改a的值，c仍然指向1 所在内存空间 
c=1                             # c 值仍然是1