tonado框架的列表嵌套 （template中for循环嵌套）

        学习了tonado框架，渐渐开始明白模板的转换，以后肯定还会遇到很多问题。。。

功能描述：

      页面显示读取的数据库父导航名称，再通过嵌套列表将子导航名称和地址查询出来，返回到页面显示，由于页面有多个父导航，父导航下又有多个子导航，所以template采用for循环嵌套，model里有两个类。两个列表关系分如下：
[pnav1, pnav2, pnav3]
pnav1.pnav_name = "父导航名1"
pnav1.cnavs = [cnav1, cnav2, cnav3]
cnav1.cnav_name = "子导航名1"
cnav1.cnav_addr = "子导航映射地址1"
cnav2.cnav_name = "子导航名2"
cnav2.cnav_addr = "子导航映射地址2"

pnav2.pnav_name = "父导航名2"
pnav2.cnavs = [cnav1, cnav2, cnav3]
cnav1.cnav_name = "父导航名2的子导航名1"
cnav1.cnav_addr = "父导航名2子导航映射地址1"
cnav2.cnav_name = "父导航名2子导航名2"
cnav2.cnav_addr = "父导航名2子导航映射地址2"

tonado-template代码片段：

{%for pnav in pnavlist %}
   <div class="panel-heading">
        <h4 class="panel-title"> <a class="a" data-toggle="collapse" data-parent="#accordion"  href="#collapseThree"> <span class="glyphicon glyphicon-plus-sign span_icon" aria-hidden="true" data-toggle="collapse" data-parent="#accordion" ></span> </a>{{pnav.pnav_name}}</h4>
   </div>
         <div id="collapseTwo" class="panel-collapse collapse in">
                <div class="panel-body">
                       {%for cnav in pnav.cnavs %}
                           <ul class="list-unstyled panel-title1">
                               <li>
                                  <span class="glyphicon glyphicon-minus-sign span_icon" aria-hidden="true" data-toggle="collapse" data-parent="#accordion" >
                                  </span>
                                  <a href="{{cnav.cnav_addr}}" class="active">{{cnav.cnav_name}}
                                  </a>
                               </li>
                           </ul>
                      {%end%}
                </div>            
             </div>
  {%end%} 

model代码：

class pnav

    def __init__(self,  pnav_name):

        self.pnav_name = pnav_name
        self.cnavs = []


class cnav

    def __init__(self,  cnav_name, cnav_addr):

        self.cnav_name = cnav_name
        self.cnav_addr = cnav_addr