Today I learned the spiders part of scrapy, the crawler name, the starting point of start_url, and the syntax of xpath:
| nodename |
Selects all child nodes of this node. |
| / |
Pick from the root node. |
| // |
Selects nodes in the document from the current node that matches the selection, regardless of their position. |
| . |
Select the current node. |
| .. |
Select the parent node of the current node. |
| @ |
Select properties. |
| bookstore |
Selects all child nodes of the bookstore element. |
| /bookstore |
Select the root element bookstore. Note: A path always represents an absolute path to an element if it starts with a forward slash ( / )! |
| bookstore/book |
Selects all book elements that are children of bookstore. |
| //book |
Selects all book child elements, regardless of their position in the document. |
| bookstore//book |
Selects all book elements that are descendants of the bookstore element, regardless of where they are located below the bookstore. |
| //@lang |
Select all properties named lang. |
| /bookstore/book[1] |
Selects the first book element that is a child element of the bookstore. |
| /bookstore/book[last()] |
Selects the last book element that is a child element of the bookstore. |
| /bookstore/book[last()-1] |
Selects the penultimate book element that is a child element of the bookstore. |
| /bookstore/book[position()<3] |
Selects the first two book elements that are children of the bookstore element. |
| //title[@lang] |
Selects all title elements that have an attribute named lang. |
| // title [@ lang = 'eng'] |
Selects all title elements that have a lang attribute with a value of eng. |
| /bookstore/book[price>35.00] |
Selects all book elements of the bookstore element, and the value of the price element must be greater than 35.00. |
| /bookstore/book[price>35.00]/title |
选取 bookstore 元素中的 book 元素的所有 title 元素，且其中的 price 元素的值须大于 35.00。 |
| * |
匹配任何元素节点。 |
| @* |
匹配任何属性节点。 |
| node() |
匹配任何类型的节点。 |
| /bookstore/* |
选取 bookstore 元素的所有子元素。 |
| //* |
选取文档中的所有元素。 |
| //title[@*] |
选取所有带有属性的 title 元素。 |
| //book/title | //book/price |
选取 book 元素的所有 title 和 price 元素。 |
| //title | //price |
选取文档中的所有 title 和 price 元素。 |
| /bookstore/book/title | //price |
选取属于 bookstore 元素的 book 元素的所有 title 元素，以及文档中所有的 price 元素。 |
XPath 轴（Axes）
轴可定义相对于当前节点的节点集。
| 轴名称 |
结果 |
| ancestor |
选取当前节点的所有先辈（父、祖父等）。 |
| ancestor-or-self |
选取当前节点的所有先辈（父、祖父等）以及当前节点本身。 |
| attribute |
选取当前节点的所有属性。 |
| child |
选取当前节点的所有子元素。 |
| descendant |
选取当前节点的所有后代元素（子、孙等）。 |
| descendant-or-self |
选取当前节点的所有后代元素（子、孙等）以及当前节点本身。 |
| following |
选取文档中当前节点的结束标签之后的所有节点。 |
| following-sibling |
选取当前节点之后的所有兄弟节点 |
| namespace |
选取当前节点的所有命名空间节点。 |
| parent |
选取当前节点的父节点。 |
| preceding |
选取文档中当前节点的开始标签之前的所有节点。 |
| preceding-sibling |
选取当前节点之前的所有同级节点。 |
| self |
选取当前节点。 |