unexpected output from difflib.SequenceMatcher

[Vlastimil Brom]

From: Vlastimil Brom <vlastimil.brom at gmail.com>
Date: 2010/4/16
Subject: unexpected output from difflib.SequenceMatcher

...
Instead of just reporting the insertion and deletion of these single
characters ... the output of the
SequenceMatcher decides to delete a large part of the string in
between the differences and to insert the almost same text after that.
...

Just for the record, althought it seemed unlikely to me first, it
turns out, that this may have the same cause like several difflib
items in the issue tracker regarding unexpected outputs for long
sequences with relatively highly repetitive items, e.g.

http://bugs.python.org/issue2986
http://bugs.python.org/issue1711800
http://bugs.python.org/issue4622
http://bugs.python.org/issue1528074

In my case, disabling the "popular" heuristics as mentioned in
http://bugs.python.org/issue1528074#msg29269
i.e. modifying the difflib source (around line 314 for py.2.5.4) to

                if 0:   # disable popular heuristics
                    if n >= 200 and len(indices) * 100 > n:
                        populardict[elt] = 1
                        del indices[:]

seems to work perfectly.
Anyway, I would appreciate comments, whether this is the appropriate
solution for the given task - i.e. the character-wise comparison of
strings; or are there maybe some drawbacks to be aware of? Wouldn't
some kind of control over the "pouplar" heuristics be useful in the
exposed interface of difflib?
Or is this just the inappropriate tool for the character-wise string
comparison, as is suggested e.g. in
http://bugs.python.org/issue1528074#msg29273  althought it seems to
work just right for the most part?

regards,
    vbr