Return a version of the query string with the _e, _k and _s values
        removed.

def filter_query_string(query):
    """
        Return a version of the query string with the _e, _k and _s values
        removed.
    """
    return '&'.join([q for q in query.split('&')
        if not (q.startswith('_k=') or q.startswith('_e=') or q.startswith('_s'))])