使用lxm访问根元素前后的处理说明

Question

使用lxml，如何访问/迭代位于根open标记之前或根close标记之后的处理指令？你知道吗

我尝试过这个方法，但是根据文档，它只在根元素中迭代：

import io

from lxml import etree

content = """\
<?before1?>
<?before2?>
<root>text</root>
<?after1?>
<?after2?>
"""

source = etree.parse(io.StringIO(content))

print(etree.tostring(source, encoding="unicode"))
# -> <?before1?><?before2?><root>text</root><?after1?><?after2?>

for node in source.iter():
    print(type(node))
# -> <class 'lxml.etree._Element'>

我唯一的解决方案是用伪元素包装XML：

dummy_content = "<dummy>{}</dummy>".format(etree.tostring(source, encoding="unicode"))
dummy = etree.parse((io.StringIO(dummy_content)))

for node in dummy.iter():
    print(type(node))
# -> <class 'lxml.etree._Element'>
#    <class 'lxml.etree._ProcessingInstruction'>
#    <class 'lxml.etree._ProcessingInstruction'>
#    <class 'lxml.etree._Element'>
#    <class 'lxml.etree._ProcessingInstruction'>
#    <class 'lxml.etree._ProcessingInstruction'>

有更好的解决办法吗？你知道吗

Answer 1

可以对根元素使用getprevious()和getnext()方法。你知道吗

before2 = source.getroot().getprevious()
before1 = before2.getprevious()

after1 = source.getroot().getnext()
after2 = after1.getnext()

见https://lxml.de/api/lxml.etree._Element-class.html。你知道吗

---

也可以使用XPath（在ElementTree或Element实例上）：

before = source.xpath("preceding-sibling::node()")  # List of two PIs
after = source.xpath("following-sibling::node()")