@app.route('/listuser/<int:user_id>', methods=['GET', 'POST'])
def update_user(user_id):
    user = User.query.get_or_404(user_id)
    form = UserUpdateForm()
    if form.validate_on_submit():
        user.name = form.name.data
        user.mail = form.mail.data
        db.session.commit()
    elif request.method == 'GET':
        form.name.data = user.name
        form.mail.data = user.mail
    return render_template('updateuser.html', form=form)

class UserUpdateForm(FlaskForm):
    name = StringField('Name', validators=[DataRequired(), Length(min=3, max=10)])
    mail = StringField('Email', validators=[DataRequired(), Email()])
    password = PasswordField('Password', validators=[DataRequired()])
    confirmpassword = PasswordField('Confirm Password', validators=[DataRequired(), EqualTo('password')])
    rights = BooleanField('Rights')
    submit = SubmitField('Update')

    def validate_mail(self, mail):
        if mail.data != self.mail.data:
            user = User.query.filter_by(mail=mail.data).first()
            raise ValidationError('That mail is already taken.')