[新手] 为什么我 Tornado 利用 html 表单的 name 值可以添加数据，但是无法删除 MongoDB 某条数据？？

class DelLiveHandler(tornado.web.RequestHandler):
def get(self):
self.render("del_live.html")
def post(self):
temp = dict()
coll = self.application.db.lives
date = self.get_argument("date", "")
city = self.get_argument("city", "")
venue = self.get_argument("venue", "")
if date != "":
temp["date"] = date
elif city != "":
temp["city"] = city
elif venue != "":
temp["venue"] = venue
coll.remove(temp)
self.redirect("/live")
上述代码操作这个表单：
{% extends "base.html" %}

{% block content %}
<fieldset>
<h3>Delete Tour Dates</h3>
<form method="post">
<p><label for="date">Date:</label>
<input type="text" id="date" name="date" value="Tour date"/></p>
<p><label for="city">City:</label>
<input type="text" id="city" name="city" value="Tour city"/></p>
<p><label for="venue">Venue:</label>
<input type="text" id="venue" name="venue" value="Tour Venue"/></p>
<input type="submit" value="Delete" id="delete">
</form>
</fieldset>
{% end %}
{% block import_js %}
<script type="text/javascript" src="{{ static_url("js/global.js") }}"></script>
<script type="text/javascript" src="{{ static_url("js/contact.js") }}"></script>
{% end %}