“//"之间的区别和“/"；在 XPath 中? [英] Difference between "//" and "/" in XPath?

问题描述

我正在尝试使用 XPath for python-selenium.

I was trying my hands on XPath for python-selenium.

我使用此链接来尝试教程中的一些 XPath:

I used this link for trying some XPaths' from tutorials:

所以我尝试了 XPaths 的这两种变体.

So I tried these two variants of XPaths'.

1. 这个表达

1. This expression

//webengagedata//preceding-sibling::*

返回 14 个结果

1. 还有这个表情

1. And this expression

//webengagedata/preceding-sibling::*

返回 9 个结果

//"如何匹配另外 5 个结果?

What does the "//" do to match 5 more results?

推荐答案

/ vs // 一般

child (/) 和 descendant-or-self (//) 都是 XPath 中的轴.

/ vs // in general

Both child (/) and descendant-or-self (//) are axes in XPath.

• / 是 /child::node()/ 的缩写.

使用 / 选择节点的直接子节点.

// 是 /descendant-or-self::node()/ 的缩写.

使用//来选择一个节点、它的子节点、它的孙节点等等递归.

Use // to select a node, its children, its grandchildren, and so on recursively.

/ vs // 与 preceding-sibling::*

/ vs // with preceding-sibling::*

您的具体问题询问了 //preceding-sibling::* 和 /preceding-sibling::* 之间的区别.

Your specific question asks about the difference between //preceding-sibling::* and /preceding-sibling::*.

由于您的数据是异地且复杂的，让我们考虑使用这种现有且更简单​​的 XML:

Since your data is offsite and complex, let's consider instead this present and simpler XML:

<r>
  <a/>
  <b>
    <c/>
    <d/>
  </b>
</r>

对于这个 XML，

1. /r/preceding-sibling::* 什么都不选，因为 r 没有前面的兄弟姐妹.
2. /r//preceding-sibling::* 选择前面的兄弟元素r 的所有后代或自 节点.即，a、b、c 和 d.(记住，/r//preceding-sibling::* 是 /descendant-or-self::node()/preceding-sibling::* 的缩写，not /descendant-or-self::*/preceding-sibling::*) 注意即使 b和d是没有元素的前辈兄弟，它们是文本节点的前辈兄弟，因为上面的XML在b 和 d.如果删除所有空格，则只会选择 a 和 c.
3. /r/descendant::*/preceding-sibling::* 选择 r 的所有后代 elements 的前面同级元素.即，a 和 c.请注意，b 和 d 未被选中，因为它们不在 r 的任何后代 元素 之前的同级元素 -- 与前面的示例不同，text 节点不符合条件.

1. /r/preceding-sibling::* selects nothing because r has no preceding siblings.
2. /r//preceding-sibling::* selects the preceding siblings elements of all of the descendant or self nodes of r. That is, a, b, c and d. (Remember, /r//preceding-sibling::* is short for /descendant-or-self::node()/preceding-sibling::*, not /descendant-or-self::*/preceding-sibling::*) Note that even though b and d are predecessor siblings to no elements, they are predecessor siblings to text nodes because the above XML has whitespace after b and d. If all whitespace were removed, then only a and c would be selected.
3. /r/descendant::*/preceding-sibling::* selects the preceding sibling elements of all descendant elements of r. That is, a and c. Note that b and d are not selected because they are not preceding sibling elements to any descendant elements of r -- unlike the previous example, text nodes do not qualify.

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