Question

I am using python 2.7 with latest lxml library. I am parsing a large XML file with very homogenous structure and millions of elements. I thought lxml’s iterparse would not build an internal tree while it parses, but apparently it does since memory usage grows until it crashes (around 1GB). Is there a way to parse large XML file using lxml without using a lot of memory?

I saw the target parser interface as one possibility, but I’m not sure if that will work any better.

Answer 1

Try using Liza Daly’s fast_iter:

def fast_iter(context, func, args=[], kwargs={}):
    # http://www.ibm.com/developerworks/xml/library/x-hiperfparse/
    # Author: Liza Daly
    for event, elem in context:
        func(elem, *args, **kwargs)
        elem.clear()
        while elem.getprevious() is not None:
            del elem.getparent()[0]
    del context

fast_iter removes elements from the tree after they have been parsed, and also previous elements (maybe with other tags) that are no longer needed.

It could be used like this:

import lxml.etree as ET
def process_element(elem):
    ...
context=ET.iterparse(filename, events=('end',), tag=...)        
fast_iter(context, process_element)