python - 当我知道我不应该能够时向元组添加元素

Question

Dive Into Python是众多消息来源之一:

You can't add elements to a tuple.

但看起来好像我被允许那样做。我的代码:

from string import find

def subStringMatchExact(target, key):
    t = (99,)
    location = find(target, key)
    while location != -1
        t += (location,)    # Why is this allowed?
        location = find(target, key, location + 1)
    return t

print subStringMatchExact("atgacatgcacaagtatgcat", "tg")

输出:

(99, 1, 6, 16)

这让我相信我在初始化 t 时实际上并没有创建元组。谁能帮我理解一下？

Answer 1

您正在将 2 个元组连接成一个新元组。您没有修改原件。

> a = (1,)
> b = a
> b == a
True
> a += (2,)
> b == a
False