给定如下html代码
<ul class="menu_block">
<li class="tabguide btn_list btnOn" data-link="authority/courses/sectionGuideBook.html"
data-key="f55ce876-fa0d-4027-9569-22ed531100a7" data-finished="true" data-disabled="false"></li>
<li class="btn-disable tabvideo" data-link="authority/courses/sectionvideo.html"
data-key="" data-finished="false" data-disabled="true"></li>
<li class="btn-disable tabmachine" data-link="authority/courses/sectionmachine.html"
data-key="" data-finished="false" data-disabled="true"></li>
<li class="tabhomework btn_list" data-link="authority/courses/sectionhomework.html"
data-key="7512c739-0d33-438a-93e8-97a77329d032" data-finished="false" data-disabled="false"></li>
</ul>
要求：使用Jquery获取data-key ！=null 的标签，然后对获取到的新标签逐一判断data-finished的值？
------解决思路----------------------
$(li:[data-key!=""]).each(fuction(k, v){
$(v).attr("data-link") // 这就是那个值 剩下的自己写吧
})