UserDoesNotExist: Instance matching query does not exist:
SQL: SELECT "t1"."id", "t1"."username", "t1"."email", "t1"."password",     "t1"."is_admin" FROM "user" AS t1 WHERE ("t1"."email" = %s)
PARAMS: [u'sharon@gmail.com']

@app.route('/register', methods=('GET', 'POST'))
def register():
    form = forms.RegisterForm()
    if form.validate_on_submit():
        if models.User.get(models.User.email == form.email.data):
            flash("user with the same email already exist")
        else:
            flash('you registered', "success")
            models.User.create_user(
            username=form.username.data,
            email=form.email.data,
            password=form.password.data)
            return redirect(url_for('login'))
    return render_template('register.html', form=form)