def _parse_pairs():
     for key, val in _cookie_parse_impl(header):
         key = to_unicode(key, charset, errors, allow_none_charset=True)
         if not key:
             continue
         val = to_unicode(val, charset, errors, allow_none_charset=True)
         yield try_coerce_native(key), val

def get_query_string(environ):
    """Returns the `QUERY_STRING` from the WSGI environment.  This also takes
    care about the WSGI decoding dance on Python 3 environments as a
    native string.  The string returned will be restricted to ASCII
    characters.

    .. versionadded:: 0.9

    :param environ: the WSGI environment object to get the query string from.
    """
    qs = wsgi_get_bytes(environ.get('QUERY_STRING', ''))
    # QUERY_STRING really should be ascii safe but some browsers
    # will send us some unicode stuff (I am looking at you IE).
    # In that case we want to urllib quote it badly.
    return try_coerce_native(url_quote(qs, safe=':&%=+$!*\'(),'))

def _url_decode_impl(pair_iter, charset, decode_keys, include_empty, errors):
    for pair in pair_iter:
        if not pair:
            continue
        s = make_literal_wrapper(pair)
        equal = s('=')
        if equal in pair:
            key, value = pair.split(equal, 1)
        else:
            if not include_empty:
                continue
            key = pair
            value = s('')
        key = url_unquote_plus(key, charset, errors)
        if charset is not None and PY2 and not decode_keys:
            key = try_coerce_native(key)
        yield key, url_unquote_plus(value, charset, errors)