app.route('/cat_html', methods=['GET'])
def categories_html(check):
    if session.get('teacher_name'):
        return trav0.gen(check)

    else:
        return redirect('/teachers')

<li class="nav-item">
    <a class="navbar-brand" href="{{ url_for('categories_html', check='sta10') }}" target="_blank" style="color:31708f;">Tasks</a>
</li>