XPath 中“//”和“/”的区别？

Question

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

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

So I tried these two variants of XPaths'.

1. This expression

   //webengagedata//preceding-sibling::*

returned 14 results

2. And this expression

   //webengagedata/preceding-sibling::*

returned 9 results

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

Answer 1

/ vs // in general

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

• / is short for /child::node()/ .

  Use / to select a node's immediate children .

• // is short for /descendant-or-self::node()/ .

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

---

/ vs // with preceding-sibling::*

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

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

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

For this XML,

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.

Answer 2

For your example

//webengagedata/preceding-sibling::* ---> returned 9 results

Because there are only 9 tags which are exact sibling of webengagedata tags thats why it is showing 9 records

//webengagedata//preceding-sibling::* ---> returned 14 results

Here it is considering child tags as well as biziclop said x/descendant-or-self::node()/y

Answer 3

The difference is that x//y is shorthand for x/descendant-or-self::node()/y .

That's all.

So while the first query selects all the descendants of <webengagedata> that have another tag after them, the second only selects the preceding siblings of the tag itself.

The rules of abbreviated xpath syntax are explained here .

Answer 4

xpath中'/'和'//'的区别是，'/'用于标识该区域内的元素，'//'用于条件后的整个页面