def _urlquote(string, safe=''):
    """
    Quotes a unicode string for use in a URL

    :param string:
        A unicode string

    :param safe:
        A unicode string of character to not encode

    :return:
        None (if string is None) or an ASCII byte string of the quoted string
    """

    if string is None or string == '':
        return None

    # Anything already hex quoted is pulled out of the URL and unquoted if
    # possible
    escapes = []
    if re.search('%[0-9a-fA-F]{2}', string):
        # Try to unquote any percent values, restoring them if they are not
        # valid UTF-8. Also, requote any safe chars since encoded versions of
        # those are functionally different than the unquoted ones.
        def _try_unescape(match):
            byte_string = unquote_to_bytes(match.group(0))
            unicode_string = byte_string.decode('utf-8', 'iriutf8')
            for safe_char in list(safe):
                unicode_string = unicode_string.replace(safe_char, '%%%02x' % ord(safe_char))
            return unicode_string
        string = re.sub('(?:%[0-9a-fA-F]{2})+', _try_unescape, string)

        # Once we have the minimal set of hex quoted values, removed them from
        # the string so that they are not double quoted
        def _extract_escape(match):
            escapes.append(match.group(0).encode('ascii'))
            return '\x00'
        string = re.sub('%[0-9a-fA-F]{2}', _extract_escape, string)

    output = urlquote(string.encode('utf-8'), safe=safe.encode('utf-8'))
    if not isinstance(output, byte_cls):
        output = output.encode('ascii')

    # Restore the existing quoted values that we extracted
    if len(escapes) > 0:
        def _return_escape(_):
            return escapes.pop(0)
        output = re.sub(b'%00', _return_escape, output)

    return output
Quotes a unicode string for use in a URL

    :param string:
        A unicode string

    :param safe:
        A unicode string of character to not encode

    :return:
        None (if string is None) or an ASCII byte string of the quoted string