human
I wrote the below code

    if (not old_text):
        old_text = ''
    if (not new_text):
        new_text = ''
    old_text = strip_tags(strip_line_breaks(unicode(old_text).encode('utf-8', errors='ignore')))
    new_text = strip_tags(strip_line_breaks(unicode(new_text).encode('utf-8', errors='ignore')))
    old_text = unicodedata.normalize('NFKD', old_text)
    new_text = unicodedata.normalize('NFKD', new_text)
    def yield_open_entry(open_entry):
        '    Yield    all    open    changes.    '
        (ls, rs) = open_entry
        if (ls[0] == rs[0]):
            (yield (False, ls[0], rs[0]))
            for (l, r) in itertools.izip_longest(ls[1:], rs[1:]):
                (yield (True, l, r))
        elif (ls[(-1)] == rs[(-1)]):
            for (l, r) in itertools.izip_longest(ls[:(-1)], rs[:(-1)]):
                (yield ((l != r), l, r))
            (yield (False, ls[(-1)], rs[(-1)]))
        else:
            for (l, r) in itertools.izip_longest(ls, rs):
                (yield (True, l, r))
    line_split = re.compile('(?:\\r?\\n)')
    dmp = diff_match_patch.diff_match_patch()
    diff = dmp.diff_main(old_text, new_text)
    dmp.diff_cleanupSemantic(diff)
    open_entry = ([None], [None])
    for (change_type, entry) in diff:
        assert (change_type in [(-1), 0, 1])
        entry = entry.replace('&', '&amp;').replace('<', '&lt;').replace('>', '&gt;')
        lines = line_split.split(entry)
        (ls, rs) = open_entry
        line = lines[0]
        if line:
            if (change_type == 0):
                ls[(-1)] = (ls[(-1)] or '')
                rs[(-1)] = (rs[(-1)] or '')
                ls[(-1)] += line
                rs[(-1)] += line
            elif (change_type == 1):
                rs[(-1)] = (rs[(-1)] or '')
                rs[(-1)] += (('<ins>%s</ins>' % line) if line else '')
            elif (change_type == (-1)):
                ls[(-1)] = (ls[(-1)] or '')
                ls[(-1)] += (('<del>%s</del>' % line) if line else '')
        lines = lines[1:]
        if lines:
            if (change_type...

What's a good function header?

=====
Here's a good function header?
assistant
#Here's a good function header.

def side_by_side_diff(old_text, new_text):