坐标轴::节点测试[预判]

# child::nodename 选取所有属于当前节点的 book 子元素，等价于 './nodename'
>>> root.xpath('child::book')
[<Element book at 0x2d888c8>, <Element book at 0x2d88878>]
>>> root.xpath('./book')
[<Element book at 0x2d888c8>, <Element book at 0x2d88878>]# attribute::lang 选取当前节点的 lang 属性，等价于 './@lang'
>>> root.xpath('//*[@lang]')[0].xpath('attribute::lang')
['eng']
>>> root.xpath('//*[@lang]')[0].xpath('@lang')
['eng']# child::* 选取当前节点的所有子元素，等价于 './*'
>>> root.xpath('child::*')
[<Element book at 0x2d88878>, <Element book at 0x2d88738>]
>>> root.xpath('./*')
[<Element book at 0x2d88878>, <Element book at 0x2d88738>]# attribute::* 选取当前节点的所有属性，等价于 './@*'
>>> root.xpath('//*[@*]')[0].xpath('attribute::*')
['eng']
>>> root.xpath('//*[@*]')[0].xpath('@*')
['eng']# child::text() 选取当前节点的所有文本子节点，等价于 './text()'
>>> root.xpath('child::text()')
['\n    ', '\n    ', '\n']
>>> root.xpath('./text()')
['\n    ', '\n    ', '\n']# child::node() 选取当前节点所有子节点，等价于 './node()'
>>> root.xpath('child::node()')
['\n    ', <Element book at 0x2d88878>, '\n    ', <Element book at 0x2d88738>, '\n']
>>> root.xpath('./node()')
['\n    ', <Element book at 0x2d88878>, '\n    ', <Element book at 0x2d88738>, '\n']# descendant::book 选取当前节点所有 book 后代，等价于 './/book'
>>> root.xpath('descendant::book')
[<Element book at 0x2d88878>, <Element book at 0x2d88738>]
>>> root.xpath('.//book')
[<Element book at 0x2d88878>, <Element book at 0x2d88738>]# ancestor::book 选取当前节点所有 book 先辈
>>> root.xpath('.//title')[0].xpath('ancestor::book')
[<Element book at 0x2d88878>]# ancestor-or-self::book 选取当前节点的所有 book 先辈以及如果当前节点是 book 的话也要选取
>>> root.xpath('.//title')[0].xpath('ancestor-or-self::book')
[<Element book at 0x2d88878>]
>>> root.xpath('.//book')[0].xpath('ancestor-or-self::book')
[<Element book at 0x2d88878>]
>>> root.xpath('.//book')[0].xpath('ancestor::book')
[]# child::*/child::price 选取当前节点的所有 price 孙节点，等价于 './*/price'
>>> root.xpath('child::*/child::price')
[<Element price at 0x2d88878>, <Element price at 0x2d88738>]
>>> root.xpath('./*/price')
[<Element price at 0x2d88878>, <Element price at 0x2d88738>]