Here is a small test case that demonstrates the problem, expected behavior and actual behavior:

{{{
for ev in xml.etree.cElementTree.iterparse(StringIO('<x></x>rubbish'), events=('start', 'end')):
    print ev
}}}

The above code should first print the two events (start and end), and then raise the exception.  In Python 2.7 it runs like this:

{{{
>>> for ev in xml.etree.cElementTree.iterparse(StringIO('<x></x>rubbish'), events=('start', 'end')):
...   print ev
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<string>", line 84, in next
cElementTree.ParseError: junk after document element: line 1, column 7
}}}

Expected behavior, obtained with my patch, is that it runs like this:

{{{
>>> for ev in my_iterparse(StringIO('<x></x>rubbish'), events=('start', 'end')):
...  print ev
... 
('start', <Element 'x' at 0xb771cba8>)
('end', <Element 'x' at 0xb771cba8>)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 26, in __iter__
cElementTree.ParseError: junk after document element: line 1, column 7
}}}

The difference is, of course, only visible when printing events.  A side-effect-free operation, such as building a list using list(iterparse(...)) would behave exactly the same before and after the change.