Question

In the post method of a RequestHandler in Tornado, self.get_argument(arg, None) gets the value of arg contained in the request.

All the examples I’ve seen return a string as value, which makes me wonder if we can send data other than strings in a POST request.

The specific use case I am interested in: I have a form with multiple fields on the page, and I want to pack a subset of its fields together in a single argument in the POST request to the server, something like

packed = self.get_argument('packed_arg', None)
arg1 = packed['arg1']
arg2 = packed['arg2']
...

while the rest of the fields are still of individual arguments. So far I’m thinking data structure similar to a dict (maybe JSON?) for this packed argument, is this feasible?

Answer 1

JSON will fit well for your purposes.

Do something like this, on client side:

var data = {'packed_arg':get_form_args(); } 

Function get_form_args() is abstraction. You can implement it any way. Javascript objects are JSONs by default.
So on client side you must create dictionary from form fields.
Think this way:

var data = {};
var names_to_pack = ['packed1', 'packed2']
$(form).find('input, select').each(function (i, x) {
    var name = $(x).attr('name')
    if(names_to_pack.indexOf(name) != -1) { 
        if(!data.packed) {
            data.packed = {};  
        }
        data['packed'][name] = $(x).val(); 
    } else { 
        data[name] = $(x).val(); 
    }
});
$.post('/', data); 

And then on server side:

raw_packed = self.get_argument('packed_arg', None)
packed = {}
if raw_packed: 
    packed = tornado.escape.json_decode(raw_packed)
arg1 = packed.get('arg1')
arg2 = packed.get('arg2')

Also you can access all POST args in self.request.arguments.