Xpath Syntax

Xpath, Python

 2018/01/01

Path 句法(URL)：

Syntax	Meaning
`tag`	Selects all child elements with the given tag. For example, `spam` selects all child elements named `spam`, and `spam/egg` selects all grandchildren named `egg` in all children named `spam`.
`*`	Selects all child elements. For example, `*/egg` selects all grandchildren named `egg`.
`.`	Selects the current node. This is mostly useful at the beginning of the path, to indicate that it’s a relative path.
`//`	Selects all subelements, on all levels beneath the current element. For example, `.//egg` selects all `egg` elements in the entire tree.
`..`	Selects the parent element.
`[@attrib]`	Selects all elements that have the given attribute.
`[@attrib='value']`	Selects all elements for which the given attribute has the given value. The value cannot contain quotes.
`[tag]`	Selects all elements that have a child named `tag`. Only immediate children are supported.
`[tag='text']`	Selects all elements that have a child named `tag` whose complete text content, including descendants, equals the given `text`.
`[position]`	Selects all elements that are located at the given position. The position can be either an integer (1 is the first position), the expression `last()` (for the last position), or a position relative to the last position (e.g. `last()-1`).

Predicates (expressions within square brackets) must be preceded by a tag name, an asterisk, or another predicate. position predicates must be preceded by a tag name.

Xpath Python使用示例：

Here’s an example that demonstrates some of the XPath capabilities of the module. We’ll be using the countrydata XML document from the Parsing XML section:

import xml.etree.ElementTree as ET
root = ET.fromstring(countrydata)
# Top-level elements
root.findall(".")
# All 'neighbor' grand-children of 'country' children of the top-level
# elements
root.findall("./country/neighbor")
# Nodes with name='Singapore' that have a 'year' child
root.findall(".//year/..[@name='Singapore']")
# 'year' nodes that are children of nodes with name='Singapore'
root.findall(".//*[@name='Singapore']/year")
# All 'neighbor' nodes that are the second child of their parent
root.findall(".//neighbor[2]")

以上示例用于XML文本，如果要作用于HTML文本，需要将 import xml.etree.ElementTree as ET 改为 import lxml.html ，以及将 root = ET.fromstring(countrydata) 改为 root = lxml.html.fromstring(HTMLData)

XPath Axes

An axis defines a node-set relative to the current node.

AxisName	Result
ancestor	Selects all ancestors (parent, grandparent, etc.) of the current node
ancestor-or-self	Selects all ancestors (parent, grandparent, etc.) of the current node and the current node itself
attribute	Selects all attributes of the current node
child	Selects all children of the current node
descendant	Selects all descendants (children, grandchildren, etc.) of the current node
descendant-or-self	Selects all descendants (children, grandchildren, etc.) of the current node and the current node itself
following	Selects everything in the document after the closing tag of the current node
following-sibling	Selects all siblings after the current node
namespace	Selects all namespace nodes of the current node
parent	Selects the parent of the current node
preceding	Selects all nodes that appear before the current node in the document, except ancestors, attribute nodes and namespace nodes
preceding-sibling	Selects all siblings before the current node
self	Selects the current node

Axe Examples

Example	Result
child::book	Selects all book nodes that are children of the current node
attribute::lang	Selects the lang attribute of the current node
child::*	Selects all element children of the current node
attribute::*	Selects all attributes of the current node
child::text()	Selects all text node children of the current node
child::node()	Selects all children of the current node
descendant::book	Selects all book descendants of the current node
ancestor::book	Selects all book ancestors of the current node
ancestor-or-self::book	Selects all book ancestors of the current node - and the current as well if it is a book node
child::*/child::price	Selects all price grandchildren of the current node

CATALOG

1. Path 句法(URL)：

XPath Axes

1. Axe Examples

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