gistfile1.py

changed_fields = document._get_changed_fields()
for field in changed_fields:
    keys = field.split('.')
    if (len(keys) == 3 and keys[0] == "comments"
            and keys[2] in document.revision_fields):
        comment_index = int(keys[1])
        old_comment = old_message.comments[comment_index]
        new_comment = document.comments[comment_index]
        revision = Revision.create(old_comment, new_comment, [keys[2]],
                                   user)
        if revision.changes:
            new_comment.revisions.append(revision)
            new_comment.updated_at = datetime.datetime.now()