Python 如何在Jinja2中设置/获取变量

我不明白，为什么这个代码不起作用：

{% set t_c = 'param_1' %}
                    <div class="col-sm-9">
                        <select id="category" name="category" class="form-control " required>
                            <option></option>
                            {% for c in categories %}
                                {% if c.id|string == org.category.id %}
                                    {% set t_c = 'param9' %}
                                    <option value="{{ c.id }}" selected>{{ c.name }} </option>
                                {% else %}
                                    <option value="{{ c.id }}">{{ c.name }} </option>
                                {% endif %}                          
                            {% endfor %}
                        </select>
                    </div>
  <input id="category_h" name="category_h" type="hidden" value="{{ t_c }}">

---

t_c='param9'

有

var   category = $("#category"),
        category_h = $("#category_h");

 category.select2();
 category_h.val(category.find("option:selected").text());