ParseError: except block cannot be attached to for block

what i try to do, is to detect if a product in a user cart has been
deleted by detecting the image in gridfs because i've duplicated the
information of this product to make it fast for the database.

here is what i did:

class AchatsHandler(BaseHandler):
    @tornado.web.authenticated
    def get(self):
        user = self.get_secure_cookie("mechtari")
        info = tornado.escape.json_decode(user)
        email = info["personnel"]["email"]
        try:
            produits = self.db.users.find({"personnel.email":email},
{"produit_down":1, "_id":0}).distinct("produit_down")
            renderer = self.fs
            error = gridfs.NoFile
        except (errors.AutoReconnect, errors.ConnectionFailure):
                self.redirect("/error")
        self.render("achats.html", produits=produits,
renderer=renderer, error=error)

{% if produits==[] %}
there is no products
{% else %}
{% try %}
{% for produit in produits %}
information about the produt
{% except error %}
this product dont exist
{% end %}
{% end %}
{% end %}

and the error:

Traceback (most recent call last):
      File "C:\Python27\lib\site-packages\tornado-2.4.post1-py2.7.egg
\tornado\web.py", line 1064, in _execute
        getattr(self, self.request.method.lower())(*args, **kwargs)
      File "C:\Python27\lib\site-packages\tornado-2.4.post1-py2.7.egg
\tornado\web.py", line 1846, in wrapper
        return method(self, *args, **kwargs)
      File "G:\Mon projet\sog-emouk\handlers.py", line 486, in get
        self.render("achats.html", produits=produits,
renderer=renderer, error=error)
      File "C:\Python27\lib\site-packages\tornado-2.4.post1-py2.7.egg
\tornado\web.py", line 515, in render
        html = self.render_string(template_name, **kwargs)
      File "C:\Python27\lib\site-packages\tornado-2.4.post1-py2.7.egg
\tornado\web.py", line 619, in render_string
        t = loader.load(template_name)
      File "C:\Python27\lib\site-packages\tornado-2.4.post1-py2.7.egg
\tornado\template.py", line 326, in load
        self.templates[name] = self._create_template(name)
      File "C:\Python27\lib\site-packages\tornado-2.4.post1-py2.7.egg
\tornado\template.py", line 358, in _create_template
        template = Template(f.read(), name=name, loader=self)
      File "C:\Python27\lib\site-packages\tornado-2.4.post1-py2.7.egg
\tornado\template.py", line 220, in __init__
        self.file = _File(self, _parse(reader, self))
      File "C:\Python27\lib\site-packages\tornado-2.4.post1-py2.7.egg
\tornado\template.py", line 831, in _parse
        block_body = _parse(reader, template, operator, in_loop)
      File "C:\Python27\lib\site-packages\tornado-2.4.post1-py2.7.egg
\tornado\template.py", line 831, in _parse
        block_body = _parse(reader, template, operator, in_loop)
      File "C:\Python27\lib\site-packages\tornado-2.4.post1-py2.7.egg
\tornado\template.py", line 825, in _parse
        block_body = _parse(reader, template, operator, operator)
      File "C:\Python27\lib\site-packages\tornado-2.4.post1-py2.7.egg
\tornado\template.py", line 777, in _parse
        raise ParseError("%s block cannot be attached to %s block" %
(operator, in_block))
    ParseError: except block cannot be attached to for block

[E 121005 18:14:19 web:1485] 500 GET /achats (::1) 12.00ms

but if i do this:

{% try %}
{% if produits==[] %}
..
{% else %}
{% for produit in produits %}
..
{% end %}
{% end %}
{% except error %}
<h2>No file!</h2>
{% end %}

i dont get the result i want; dot get "no file!" and the product is
shown!