try: except:

@app.route("/signup", methods=["GET", "POST"])
@templated("signup.html")
def signup_user():
    """
    Signup-page with validating on POST request and commiting new user if all data is valid.
    @return: If validated and signed up - redirecting to index-page, if trying to add existing user,
    refresh page with message, otherwise - rendiring page with form (like simply GET request).
    """
    form = RegForm()
    try:
        if form.validate_on_submit():
            user = User(grup="user", regd=datetime.now())
            form.populate_obj(user)
            db.session.add(user)
            db.session.commit()
            return redirect("/index")
        return dict(title="Tell us about you...", form=form)
    except IntegrityError:
        return dict(title="Tell us about you...", form=form, message="User with such email already exists")