def anon_session_score(session, to_add=0, possible=0):
    """
    Returns the session score for non-signed in users.
    If number passed in then add this to the running total and
    return session score.

    examples:
        anon_session_score(1, 1) will add 1 out of a possible 1
        anon_session_score(0, 2) will add 0 out of a possible 2
        x, y = anon_session_score() will return the session score
                                    without modification

    Left this as an individual function for unit testing
    """
    if "session_score" not in session:
        session["session_score"], session["session_score_possible"] = 0, 0

    if possible > 0:
        session["session_score"] += to_add
        session["session_score_possible"] += possible

    return session["session_score"], session["session_score_possible"]