Parsing huge, badly encoded XML files in Python

Question

I have been working on code that parses external XML-files. Some of these files are huge, up to gigabytes of data. Needless to say, these files need to be parsed as a stream because loading them into memory is much too inefficient and often leads to OutOfMemory troubles.

I have used the libraries miniDOM, ElementTree, cElementTree and I am currently using lxml. Right now I have a working, pretty memory-efficient script, using lxml.etree.iterparse. The problem is that some of the XML files I need to parse contain encoding errors (they advertise as UTF-8, but contain differently encoded characters). When using lxml.etree.parse this can be fixed by using the recover=True option of a custom parser, but iterparse does not accept a custom parser. (see also: this question)

My current code looks like this:

from lxml import etree
events = ("start", "end")
context = etree.iterparse(xmlfile, events=events)
event, root_element = context.next() # <items>
for action, element in context:
    if action == 'end' and element.tag == 'item':
    # <parse>
    root_element.clear() 

Error when iterparse encounters a bad character (in this case, it's a ^Y):

lxml.etree.XMLSyntaxError: Input is not proper UTF-8, indicate encoding !
Bytes: 0x19 0x73 0x20 0x65, line 949490, column 25

I don't even wish to decode this data, I can just drop it. However I don't know any way to skip the element - I tried context.next and continue in try/except statements.

Any help would be appreciated!

Update

Some additional info: This is the line where iterparse fails:

<description><![CDATA:[musea de la photographie fonds mercator. Met meer dan 80.000 foto^Ys en 3 miljoen negatieven is het Muse de la...]]></description>

According to etree, the error occurs at bytes 0x19 0x73 0x20 0x65.
According to hexedit, 19 73 20 65 translates to ASCII .s e
The . in this place should be an apostrophe (foto's).

I also found this question, which does not provide a solution.

Answer 1

If the problems are actual character encoding problems, rather than malformed XML, the easiest, and probably most efficient, solution is to deal with it at the file reading point. Like this:

import codecs
from lxml import etree
events = ("start", "end")
reader = codecs.EncodedFile(xmlfile, 'utf8', 'utf8', 'replace')
context = etree.iterparse(reader, events=events)

This will cause the non-UTF8-readable bytes to be replaced by '?'. There are a few other options; see the documentation for the codecs module for more.