python - python中的lxml iterparse无法处理命名空间

Question

from lxml import etree
import StringIO

data= StringIO.StringIO('<root xmlns="http://some.random.schema"><a>One</a><a>Two</a><a>Three</a></root>')
docs = etree.iterparse(data,tag='a')
a,b = docs.next()


Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "iterparse.pxi", line 478, in lxml.etree.iterparse.__next__ (src/lxml/lxml.etree.c:95348)
  File "iterparse.pxi", line 534, in lxml.etree.iterparse._read_more_events (src/lxml/lxml.etree.c:95938)
StopIteration

工作正常，直到我将命名空间添加到根节点。关于我可以做些什么作为解决方法或正确的方法的任何想法？由于文件非常大，我需要事件驱动。

Answer 1

当附加命名空间时，标签不是a，而是{http://some.random.schema}a. 试试这个（Python 3）：

from lxml import etree
from io import BytesIO

xml = '''\
<root xmlns="http://some.random.schema">
  <a>One</a>
  <a>Two</a>
  <a>Three</a>
</root>'''
data = BytesIO(xml.encode())
docs = etree.iterparse(data, tag='{http://some.random.schema}a')
for event, elem in docs:
    print(f'{event}: {elem}')

或者，在 Python 2 中：

from lxml import etree
from StringIO import StringIO

xml = '''\
<root xmlns="http://some.random.schema">
  <a>One</a>
  <a>Two</a>
  <a>Three</a>
</root>'''
data = StringIO(xml)
docs = etree.iterparse(data, tag='{http://some.random.schema}a')
for event, elem in docs:
    print event, elem

这会打印出类似的内容：

end: <Element {http://some.random.schema}a at 0x10941e730>
end: <Element {http://some.random.schema}a at 0x10941e8c0>
end: <Element {http://some.random.schema}a at 0x10941e960>

正如@mihail-shcheglov 指出的那样，*也可以使用通配符，它​​适用于任何名称空间或没有名称空间：

from lxml import etree
from io import BytesIO

xml = '''\
<root xmlns="http://some.random.schema">
  <a>One</a>
  <a>Two</a>
  <a>Three</a>
</root>'''
data = BytesIO(xml.encode())
docs = etree.iterparse(data, tag='{*}a')
for event, elem in docs:
    print(f'{event}: {elem}')

有关更多信息，请参阅lxml.etree 文档。

Answer 2

为什么不用正则表达式？

1)

使用 lxml 比使用正则表达式慢。

from time import clock
import StringIO



from lxml import etree

times1 = []
for i in xrange(1000):
    data= StringIO.StringIO('<root ><a>One</a><a>Two</a><a>Three\nlittle pigs</a><b>Four</b><a>another</a></root>')
    te = clock()
    docs = etree.iterparse(data,tag='a')
    tf = clock()
    times1.append(tf-te)
print min(times1)

print [etree.tostring(y) for x,y in docs]




import re

regx = re.compile('<a>[\s\S]*?</a>')

times2 = []
for i in xrange(1000):
    data= StringIO.StringIO('<root ><a>One</a><a>Two</a><a>Three\nlittle pigs</a><b>Four</b><a>another</a></root>')
    te = clock()
    li = regx.findall(data.read())
    tf = clock()
    times2.append(tf-te)
print min(times2)

print li

结果

0.000150298431784
['<a>One</a>', '<a>Two</a>', '<a>Three\nlittle pigs</a>', '<a>another</a>']
2.40253998762e-05
['<a>One</a>', '<a>Two</a>', '<a>Three\nlittle pigs</a>', '<a>another</a>']

0.000150298431784 / 2.40253998762e-05 是 6.25
lxml 比正则表达式慢 6.25 倍

.

2)

如果命名空间没有问题：

import StringIO
import re

regx = re.compile('<a>[\s\S]*?</a>')

data= StringIO.StringIO('<root xmlns="http://some.random.schema"><a>One</a><a>Two</a><a>Three\nlittle pigs</a><b>Four</b><a>another</a></root>')
print regx.findall(data.read())

结果

['<a>One</a>', '<a>Two</a>', '<a>Three\nlittle pigs</a>', '<a>another</a>']