python - 如何理解这个结果？

Question

我是 Python 新手。这是我对列表的一个问题:据说列表是可变的而元组是不可变的。但是当我写下以下内容时:

L1 = [1, 2, 3]
L2 = (L1, L1)
L1[1] = 5
print L2

结果是

([1, 5, 3], [1, 5, 3])

代替

([1, 2, 3], [1, 2, 3])

但是 L2 是一个元组，而且元组是不可变的。为什么当我改变L1的值时，L2的值也改变了？

Answer 1

来自 Python 文档 (http://docs.python.org/reference/datamodel.html)，注意:

The value of an immutable container object that contains a reference to a mutable object can change when the latter’s value is changed; however the container is still considered immutable, because the collection of objects it contains cannot be changed. So, immutability is not strictly the same as having an unchangeable value, it is more subtle.