将数字 1 添加到集合中没有效果

Adding the number 1 to a set has no effect(将数字 1 添加到集合中没有效果)

问题描述

我无法将整数 1 添加到现有集合中.在交互式外壳中，这就是我正在做的事情:

I cannot add the integer number 1 to an existing set. In an interactive shell, this is what I am doing:

>>> st = {'a', True, 'Vanilla'}
>>> st
{'a', True, 'Vanilla'}
>>> st.add(1)
>>> st
{'a', True, 'Vanilla'}   # Here's the problem; there's no 1, but anything else works
>>> st.add(2)
>>> st
{'a', True, 'Vanilla', 2}

这个问题是两个月前发布的，但我认为它被误解了.我正在使用 Python 3.2.3.

This question was posted two months ago, but I believe it was misunderstood. I am using Python 3.2.3.

推荐答案

>>> 1 == True
True

我相信你的问题是 1 和 True 是相同的值，所以 1 是已经在集合中".

I believe your problem is that 1 and True are the same value, so 1 is "already in the set".

>>> st
{'a', True, 'Vanilla'}
>>> 1 in st
True

在数学运算中，True 本身被视为 1:

In mathematical operations True is itself treated as 1:

>>> 5 + True
6
>>> True * 2
2
>>> 3. / (True + True)
1.5

虽然 True 是 bool 而 1 是 int:

Though True is a bool and 1 is an int:

>>> type(True)
<class 'bool'>
>>> type(1)
<class 'int'>

因为 1 in st 返回 True，我认为您应该没有任何问题.这是一个非常奇怪的结果.如果您有兴趣进一步阅读，@Lattyware 指向 PEP 285深入解释了这个问题.

Because 1 in st returns True, I think you shouldn't have any problems with it. It is a very strange result though. If you're interested in further reading, @Lattyware points to PEP 285 which explains this issue in depth.

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