Python Reptile --Xpath (b)

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3, Xpath shaft

Axis defines the relationship between the selected node tree with the current node.

Absolute location path, relative location path

Absolute location path starting at the forward slash "/", the path is not a relative position.

Step (step)

Location path comprises one or more steps, each step are divided slash: / step / step / ... (absolute position path), step / step / ... (the relative position of the path).
Step syntax: 轴名称::节点测试[谓语]
the set of nodes (axis name) used in the Xpath axis:

Axis name	meaning
child	Select all the child elements of the current node
parent	Select the parent of the current node
descendant	Select all descendants of the current node elements (descendants, etc.)
ancestor	Select all the ancestors of the current node (grandfather, father, etc.)
descendant-or-self	Select all descendants of the current node elements (descendants, etc.) as well as the current node itself
ancestor-or-self	Select all the ancestors of the current node (grandfather, father, etc.) as well as the current node itself
preceding-sibling	Prior to the selection of the current node all of the peer nodes
following-sibling	All siblings after the current node selection
preceding	All nodes before the start tag of the current node selected document
following	All nodes after the end of the tab, select the document in the current node
self	Select the current node
attribute	Select all attributes of the current node
namespace	Select all the namespace of the current node

Let's look at an example:

<xml version="1.0" encoding="ISO-8859-1">
<classroom>
    <student>
        <id>1001</id>
        <name lang="en">marry</name>
        <age>20</age>
        <country>China</country>
    </student>
    <student>
        <id>1002</id>
        <name lang="en">jack</name>
        <age>25</age>
        <country>USA</country>
    </student>
    <teacher>
        <classid>1<classid>
        <name lang="en">tom</name>
        <age>50</age>
        <country>USA</country>
    </teacher>
</classroom>

Achieve results	Path expression
Child elements currently selected node teacher node calssroom	/classroom/child::teacher
Select all the parent node id	//id/parent::*
Select all ancestor nodes as child nodes classid	//classid/ancestor::*
Select all descendants of nodes in the classroom node	/classroom/descendant::*
All the student to select parent node id element	//student/descendant::id
Select all the elements classid ancestor node and itself	//classid/ancestor-or-self::*
Select / classroom / student itself and all descendant elements	/classroom/student/descendant-or-self::*
Select all siblings before / classroom / teacher, the result is all the student selected nodes	/classroom/teacher/preceding-sibling::*
Select all siblings / classroom student after the second, the result is the selected node teacher	/classroom/student[2]/following-sibling::*
Node (in addition to their ancestors), not only the student node, and child node before which all selected / classroom / teacher node	/classroom/teacher/preceding::*
Select / classroom all the nodes after the second student, the teacher result is selected nodes and child nodes	/classroom/student[2]/following::*
Student select node, no means alone, primarily used in conjunction with other axes, such as the ancestor-or-self, descendant-or-self	//student/self::*
Select all the attributes / classroom / teacher / name node	/classroom/teacher/name/attrubute::*