有意思的元组ID，求解。

今天看python过程中遇到一个问题，比较疑惑。
元组aee = (1,2,3)， 执行aee += ()后， id改变为值Ａ。再执行aee += ()，　id改变为值B， 再执行aee += ()， id又变为值A。 继续执行，id在A和B之间切换。 这是为什么？

先上代码：

def test():
    aee = (1,2,3)
    print ("1:", aee)
    print ("id_1:", id(aee))
     
    aee += ()
    print ("2:", aee)
    print ("id_2:", id(aee))
    
    aee += ()
    print ("3:", aee)
    print ("id_3:", id(aee))
    
    aee += ()
    print ("4:", aee)
    print ("id_4:", id(aee))
    
    aee += ()
    print ("5:", aee)
    print ("id_5:", id(aee))

if __name__ == "__main__":
    test()

运行结果：

λ python3 C:\Users\qingfang\Desktop\test20180628.py
1: (1, 2, 3)
id_1: 2554181486200
2: (1, 2, 3)
id_2: 2554181486344     # id A
3: (1, 2, 3)
id_3: 2554181417648   # id B
4: (1, 2, 3)
id_4: 2554181486344   # id A
5: (1, 2, 3)
id_5: 2554181417648   # id B

中间添加一个元组，查看id是否有改变？

def test():
    aee = (1,2,3)
    print ("1:", aee)
    print ("id_1:", id(aee))
    
    aee += ()
    print ("2:", aee)
    print ("id_2:", id(aee))
    
    aee += ()
    print ("3:", aee)
    print ("id_3:", id(aee))
    
    abb = (2,3,4)            #测试代码
    print ("abb:", abb)
    print ("id_abb:", id(abb))
    
    aee += ()
    print ("4:", aee)
    print ("id_4:", id(aee))
    
    aee += ()
    print ("5:", aee)
    print ("id_5:", id(aee))

if __name__ == "__main__":
    test()

运行结果：

λ python3 C:\Users\qingfang\Desktop\test20180628.py
1: (1, 2, 3)
id_1: 2760120043128
2: (1, 2, 3)
id_2: 2760119974576   # id A
3: (1, 2, 3)
id_3: 2760120076832 # id B
abb: (2, 3, 4)
id_abb: 2760120043272   # 添加的变量 Id
4: (1, 2, 3)
id_4: 2760119974576 # id A
5: (1, 2, 3)
id_5: 2760120076832 # id B

还是相同的。