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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def logout():
 """ When the user accesses this route they are logged out. """


    cas_username_session_key = current_app.config['CAS_USERNAME_SESSION_KEY']
    cas_attributes_session_key = current_app.config['CAS_ATTRIBUTES_SESSION_KEY']

    if cas_username_session_key in flask.session:
        del flask.session[cas_username_session_key]

    if cas_attributes_session_key in flask.session:
        del flask.session[cas_attributes_session_key]

    if(current_app.config['CAS_AFTER_LOGOUT'] is not None):
        redirect_url = create_cas_logout_url(
            current_app.config['CAS_SERVER'],
            current_app.config['CAS_LOGOUT_ROUTE'],
            current_app.config['CAS_AFTER_LOGOUT'])
    else:
        redirect_url = create_cas_logout_url(
            current_app.config['CAS_SERVER'],
            current_app.config['CAS_LOGOUT_ROUTE'])

    current_app.logger.debug('Redirecting to: {0}'.format(redirect_url))
    return flask.redirect(redirect_url)