Get better parse error message from ElementTree

Question

If I try to parse a broken XML the exception shows the line number. Is there a way to show the XML context?

I want to see the xml tags before and after the broken part.

Example:

import xml.etree.ElementTree as ET
tree = ET.fromstring('<a><b></a>')

Exception:

Traceback (most recent call last):
  File "tmp/foo.py", line 2, in <module>
    tree = ET.fromstring('<a><b></a>')
  File "/usr/lib/python2.7/xml/etree/ElementTree.py", line 1300, in XML
    parser.feed(text)
  File "/usr/lib/python2.7/xml/etree/ElementTree.py", line 1642, in feed
    self._raiseerror(v)
  File "/usr/lib/python2.7/xml/etree/ElementTree.py", line 1506, in _raiseerror
    raise err
xml.etree.ElementTree.ParseError: mismatched tag: line 1, column 8

Something like this would be nice:

ParseError:
<a><b></a>
=====^

unutbu · Accepted Answer · 2016-12-16 10:44:37Z

16

You could make a helper function to do this:

import sys
import io
import itertools as IT
import xml.etree.ElementTree as ET
PY2 = sys.version_info[0] == 2
StringIO = io.BytesIO if PY2 else io.StringIO

def myfromstring(content):
    try:
        tree = ET.fromstring(content)
    except ET.ParseError as err:
        lineno, column = err.position
        line = next(IT.islice(StringIO(content), lineno))
        caret = '{:=>{}}'.format('^', column)
        err.msg = '{}\n{}\n{}'.format(err, line, caret)
        raise 
    return tree

myfromstring('<a><b></a>')

yields

xml.etree.ElementTree.ParseError: mismatched tag: line 1, column 8
<a><b></a>
=======^

edited Dec 16, 2016 at 10:44

answered Jan 5, 2015 at 12:44

unutbu

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4 Comments

Kobi K Over a year ago

up-vote for using err.position didn't know about that.

unutbu Over a year ago

@KobiK: I didn't know either, but a good introspection tool, like IPython, comes in handy to discover what's available in objects like err.

guettli Over a year ago

Thank you very much. Works nice.

FooBar Over a year ago

In Python 3, you wil lneed to replace io.BytesIO with io.StringIO

Kobi K · Accepted Answer · 2015-01-05 12:38:15Z

2

It's not the best option but it's easy and simple, you can just parse the ParseError Extract the line and column and then use it to show where is the problem.

import xml.etree.ElementTree as ET
from xml.etree.ElementTree import ParseError
my_string = '<a><b><c></b></a>'
try:
    tree = ET.fromstring(my_string)
except ParseError as e:
    formatted_e = str(e)
    line = int(formatted_e[formatted_e.find("line ") + 5: formatted_e.find(",")])
    column = int(formatted_e[formatted_e.find("column ") + 7:])
    split_str = my_string.split("\n")
    print "{}\n{}^".format(split_str[line - 1], len(split_str[line - 1][0:column])*"-")

Note: the \n is just for the example you need to split it the right way.

answered Jan 5, 2015 at 12:38

Kobi K

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