Are there any XML parsers for Python that can parse file streams? My XML files are too big to fit in memory, so I need to parse the stream.
Ideally I wouldn't have to have root access to install things, so lxml is not a very good option.
I have been using xml.etree.ElementTree but I am convinced it is broken.
Here's good answer about xml.etree.ElementTree.iterparse practice on huge XML files. lxml has the method as well. The key to stream parsing with iterparse is manual clearing and removing already processed nodes, because otherwise you will end up running out of memory.
Another option is using xml.sax. The official manual is too formal to me, and lacks examples so it needs clarification along with the question. Default parser module, xml.sax.expatreader, implement incremental parsing interface xml.sax.xmlreader.IncrementalParser. That is to say xml.sax.make_parser() provides suitable stream parser.
For instance, given a XML stream like:
<?xml version="1.0" encoding="utf-8"?>
<root>
<entry><a>value 0</a><b foo='bar' /></entry>
<entry><a>value 1</a><b foo='baz' /></entry>
<entry><a>value 2</a><b foo='quz' /></entry>
...
</root>
Can be handled in the following way.
#!/usr/bin/env python
# -*- coding: utf-8 -*-
import xml.sax
class StreamHandler(xml.sax.handler.ContentHandler):
lastEntry = None
lastName = None
def startElement(self, name, attrs):
self.lastName = name
if name == 'entry':
self.lastEntry = {}
elif name != 'root':
self.lastEntry[name] = {'attrs': attrs, 'content': ''}
def endElement(self, name):
if name == 'entry':
print({
'a' : self.lastEntry['a']['content'],
'b' : self.lastEntry['b']['attrs'].getValue('foo')
})
self.lastEntry = None
elif name == 'root':
raise StopIteration
def characters(self, content):
if self.lastEntry:
self.lastEntry[self.lastName]['content'] += content
if __name__ == '__main__':
# use default ``xml.sax.expatreader``
parser = xml.sax.make_parser()
parser.setContentHandler(StreamHandler())
# feed the parser with small chunks to simulate
with open('data.xml') as f:
while True:
buffer = f.read(16)
if buffer:
try:
parser.feed(buffer)
except StopIteration:
break
# if you can provide a file-like object it's as simple as
with open('data.xml') as f:
parser.parse(f)
Use xml.etree.cElementTree. It's much faster than xml.etree.ElementTree. Neither of them are broken. Your files are broken (see my answer to your other question).
