Why is ElementTree raising a ParseError?

Question

I have been trying to parse a file with xml.etree.ElementTree:

import xml.etree.ElementTree as ET
from xml.etree.ElementTree import ParseError

def analyze(xml):
    it = ET.iterparse(file(xml))
    count = 0
    last = None

    try:        
        for (ev, el) in it:
            count += 1
            last = el

    except ParseError:
            print("catastrophic failure")
            print("last successful: {0}".format(last))

    print('count: {0}'.format(count))

This is of course a simplified version of my code, but this is enough to break my program. I get this error with some files if I remove the try-catch block:

Traceback (most recent call last):
  File "<pyshell#22>", line 1, in <module>
    from yparse import analyze; analyze('file.xml')
  File "C:\Python27\yparse.py", line 10, in analyze
    for (ev, el) in it:
  File "C:\Python27\lib\xml\etree\ElementTree.py", line 1258, in next
    self._parser.feed(data)
  File "C:\Python27\lib\xml\etree\ElementTree.py", line 1624, in feed
    self._raiseerror(v)
  File "C:\Python27\lib\xml\etree\ElementTree.py", line 1488, in _raiseerror
    raise err
ParseError: reference to invalid character number: line 1, column 52459

The results are deterministic though, if a file works it will always work. If a file fails, it always fails and always fails at the same point.

The strangest thing is I'm using the trace to find out if I have any malformed XML that's breaking the parser. I then isolate the node that caused the failure. But when I create an XML file containing that node and a few of its neighbors, the parsing works!

This doesn't seem to be a size problem either. I have managed to parse much larger files with no problems.

Any ideas?

Answer 1

I'm not sure if this answers your question, but if you want to use an exception with the ParseError raised by element tree, you would do this:

except ET.ParseError:
            print("catastrophic failure")
            print("last successful: {0}".format(last))

Source: http://effbot.org/zone/elementtree-13-intro.htm