can't get multi-select field name when post (no choice)
<p>html:</p>

<pre><code>&lt;form method="post"&gt;{% module xsrf_form_html() %}
    &lt;input name="username" type="text"&gt;
    &lt;select name="ss" multiple&gt;
        &lt;option value="1"&gt;hello&lt;/option&gt;
        &lt;option value="2"&gt;word&lt;/option&gt;
    &lt;/select&gt;
    &lt;button type="submit"&gt;æäº¤&lt;/button&gt;
&lt;/form&gt;
</code></pre>

<p>tornado:</p>

<pre><code>class TestMultiSelectEmptyPost(BaseHandler):

    def get(self, *args, **kwargs):
        self.render('multi-select-empty-post.html')

    def post(self, *args, **kwargs):
        print self.request.arguments
</code></pre>

<p>browser:
<a href="http://i.stack.imgur.com/i6MLo.png" rel="nofollow">enter image description here</a></p>

<p>server return:</p>

<pre><code>{'username': ['aaaa'], '_xsrf': ['xxx|xxx|xxx|xxx']}
</code></pre>

<p>multi-select field name "ss" is missing</p>

<p>To determine whether the user selected <strong>none</strong> of the options, do:</p>

<pre><code>ss = self.request.arguments.get("ss")
</code></pre>

<p>The <code>get</code> method returns <code>None</code> if there is no value. So,</p>

<pre><code>if ss is None:
    print("User selected nothing")
else:
    print("ss = %s" % ss)
</code></pre>

python html tornado multi-select