9

我需要解析一个非常大（~40GB）的 XML 文件，从中删除某些元素，然后将结果写入一个新的 xml 文件。我一直在尝试使用 python 的 ElementTree 中的 iterparse，但我对如何修改树然后将生成的树写入新的 XML 文件感到困惑。我已经阅读了 itertree 上的文档，但还没有弄清楚。有什么简单的方法可以做到这一点吗？

谢谢！

编辑：这是我到目前为止所拥有的。

import xml.etree.ElementTree as ET
import re 

date_pages = []
f=open('dates_texts.xml', 'w+')

tree = ET.iterparse("sample.xml")

for i, element in tree:
    if element.tag == 'page':
        for page_element in element:
            if page_element.tag == 'revision':
                for revision_element in page_element:
                    if revision_element.tag == '{text':
                        if len(re.findall('20\d\d', revision_element.text.encode('utf8'))) == 0:
                            element.clear()
4

2 回答 2

8

If you have a large xml that doesn't fit in memory then you could try to serialize it one element at a time. For example, assuming <root><page/><page/><page/>...</root> document structure and ignoring possible namespace issues:

import xml.etree.cElementTree as etree

def getelements(filename_or_file, tag):
    context = iter(etree.iterparse(filename_or_file, events=('start', 'end')))
    _, root = next(context) # get root element
    for event, elem in context:
        if event == 'end' and elem.tag == tag:
            yield elem
            root.clear() # free memory

with open('output.xml', 'wb') as file:
    # start root
    file.write(b'<root>')

    for page in getelements('sample.xml', 'page'):
        if keep(page):
            file.write(etree.tostring(page, encoding='utf-8'))

    # close root
    file.write(b'</root>')

where keep(page) returns True if page should be kept e.g.:

import re

def keep(page):
    # all <revision> elements must have 20xx in them
    return all(re.search(r'20\d\d', rev.text)
               for rev in page.iterfind('revision'))

For comparison, to modify a small xml file, you could:

# parse small xml
tree = etree.parse('sample.xml')

# remove some root/page elements from xml
root = tree.getroot()
for page in root.findall('page'):
    if not keep(page):
        root.remove(page) # modify inplace

# write to a file modified xml tree
tree.write('output.xml', encoding='utf-8')
于 2013-03-17T03:59:51.873 回答
1

Perhaps the answer to my similar question can help you out.

As for how to write this back to an .xml file, I ended up doing this at the bottom of my script:

with open('File.xml', 'w') as t: # I'd suggest using a different file name here than your original
    for line in ET.tostring(doc):
        t.write(line)
    t.close
print('File.xml Complete') # Console message that file wrote successfully, can be omitted

The variable doc is from earlier on in my script, comparable to where you have tree = ET.iterparse("sample.xml") I have this:

doc = ET.parse(filename)

I've been using lxml instead of ElementTree but I think the write out part should still work (I think it's mainly just xpath stuff that ElementTree can't handle.) I'm using lxml imported with this line:

from lxml import etree as ET

Hopefully this (along with my linked question for some additional code context if you need it) can help you out!

于 2013-03-17T02:08:38.237 回答