python中的lxml iterparse不能处理名称空间

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

在我将命名空间添加到根节点之前，它工作得很好。有没有关于我可以做些什么的想法，或者是做这件事的正确方法？我需要事件驱动，因为非常大的文件。

Answer 1

如果附加了名称空间，则标记不是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

这将打印类似以下内容：

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不适用于任何名称空间：

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}')

有关详细信息，请参阅lxml.etree docs。

Answer 2

为什么不使用正则表达式呢？

1)

使用lxml比使用regex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为6.25

lxml比regex慢6.25倍

。

2)

如果名称空间：

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>']