How to use the changelog.Change function in changelog

if changelog.versions:
            last_version = changelog.versions[0]
            print >> sys.stderr, "INFO: Last version is '%s'." % (
                last_version.name)
            try:
                last_tag = gitlab.get(
                    'repository/tags/%s' % last_version.name
                )
            except:
                print >> sys.stderr, ("ERROR: Can't find previous release "
                                      "'%s' on Gitlab." % last_version.name)
                raise
            since = dateutil.parser.parse(last_tag['commit']['committed_date'])
        mrs = get_mrs(gitlab, branches=args.branches, since=since)
        for mr in mrs:
            version.changes.append(Change(mr['title'], mr=mr['iid']))
        text = version.to_string()
        if last_version is not None and last_version.prerelease:
            for change in last_version.changes:
                text += '%s\n' % change.to_string()
            changelog.versions.pop(0)
        while True:
            text = editor(text, tmp_suffix='.md')
            try:
                version = Version.from_string(text)
            except Exception as exc:
                print >> sys.stderr, "WARNING: Error parsing change: %r" % exc
                if not prompt_boolean("Re-edit changelog", default=True):
                    print >> sys.stderr, "ERROR: Exiting."
                    sys.exit(1)
            else:
                break

if changelog.versions:
            last_version = changelog.versions[0]
            print >> sys.stderr, "INFO: Last version is '%s'." % (
                last_version.name)
            try:
                last_tag = gitlab.get(
                    'repository/tags/%s' % last_version.name
                )
            except:
                print >> sys.stderr, ("ERROR: Can't find previous release "
                                      "'%s' on Gitlab." % last_version.name)
                raise
            since = dateutil.parser.parse(last_tag['commit']['committed_date'])
        mrs = get_mrs(gitlab, branches=args.branches, since=since)
        for mr in mrs:
            version.changes.append(Change(mr['title'], mr=mr['iid']))
        text = version.to_string()
        if last_version is not None and last_version.prerelease:
            for change in last_version.changes:
                text += '%s\n' % change.to_string()
            changelog.versions.pop(0)
        while True:
            text = editor(text, tmp_suffix='.md')
            try:
                version = Version.from_string(text)
            except Exception as exc:
                print >> sys.stderr, "WARNING: Error parsing change: %r" % exc
                if not prompt_boolean("Re-edit changelog", default=True):
                    print >> sys.stderr, "ERROR: Exiting."
                    sys.exit(1)
            else:
                break