为什么“ test” .count（''）返回5？ [英] Why does "test".count('') return 5?

问题描述

这是一个简短的例子，但很烦人。我知道我可以计算一个字符串在另一个这样的字符串中出现的次数：

This is a short one, yet very irritating. I know I can count the amount of times a string occurs within another string like this:

'banana'.count('a')
>>>3

表示香蕉包含字母 a 3次。

在这里

我的第一个困惑是-当我执行'foo'.count（''）时，

My first confusion is - when I do 'foo'.count(''), what does Python look for?

是'' == None ==什么吗？

is '' == None == anything?

似乎并非如此，但是''在逻辑上又是什么呢？而且更重要的是，为什么

It doesn't seem to be the case, but then again, what IS '' logically speaking? And more importantly, why does

'test'.count('')
>>>5

返回比字符串长度多一的字符串吗？

return one more than the length of the string?

始终比字母数量高1的字符串包含什么？

What the hell is included in a string that's always 1 higher than the amount of letters? the void?

编辑：'字符两次看起来像一个 字符。我在这里说两次'以避免混淆

the ' character twice looks like one " character. I am talking about two times ' here, to avoid confusion

EDIT2：对''的金额如何产生混淆。请参阅下面的评论。

There seems to be some confusion about how the amount of '' happen. Refer to comments below.

推荐答案

每个字符串 ¹ 都可以认为是：

Every string¹ can be thought of as:

any_string = "" + "".join(any_string) + ""

其中包含 len （any_string）+ 1个''实例。

对于 foo ，例如：

"" + "f" + "" + "o" + "" + "o"+ ""
#    |----- from join -------|

可以看到，有 4 个实例 在中。

As it can be seen there are 4 instances of "" in it.

请注意，这是否答案或所有答案可以通过某种方式为自己辩护。这是哲学上的：

Note however, that this is a problem where no answer or all answers could somehow support a case for themselves. It get's philosophical:

• 什么都不包含什么？


• 某物中不含多少东西？

• How much nothing is contained in nothing?
• How much nothing is contained in something?

此答案试图解释Python使用的约定并不打算暗示这是所有语言都采用的方式\应该这样做； 这就是Python的工作方式。

This answer tries to explain the convention used by Python and does not intend to suggest that this is the way all languages do it \ should be doing it; it is just how Python does it.

¹ Empty字符串是一个例外，并且处理方式不同；他们只是返回 1 ;这又是另一个约定。

¹Empty strings are an exception and are handled differently; they simply return 1; which is yet another convention.

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