converting a JSON string back to an array

Question

I'm passing a 2-dimensional array of float values to my views.py via ajax. My ajax call looks like this:

$.ajax({
          method: "POST",
          url: "introURL",
          data: {
            csrfmiddlewaretoken: document.getElementsByName('csrfmiddlewaretoken')[0].value,
            dsg_mtx : JSON.stringify(dsg_mtx),

           },
          success: function(data) {

            document.getElementById("test").innerHTML = data;  // echo response
          },
          error: function() {
            alert ("Something went wrong");
          }

I'm pulling my data to the view with this call:

def introURL(request):
    if request.is_ajax():
        try:
            designMtx = json.loads(request.POST['dsg_mtx'], parse_float=None)

        except KeyError:
            return HttpResponse('Error, intro import') 

        ... Some transformation of designMtx...


        return HttpResponse(response)       
    else:
        raise Http404

so my question is how do I convert this json stringify'd object back to a 2-dimensional array which I can use to compute a response? As you can see I tried using the parse_float option, but it's still a str data type.

the array being passed, dsg_mtx, is created with a Handson tables and looks like this:

Thanks for your guidance.

Before $.ajax add console.log(dsg_mtx) and show what is in console. In the same way in Python code before json.loads add print request.POST['dsg_mtx'] and show whats is in output. — Tomasz Jakub Rup
– Tomasz Jakub Rup, Commented Nov 7, 2015 at 6:08
I think I see the issue... my Handson table is initiated as 2dimensional array of numbers, but as soon as I type anything in a cell it converts the value in that cell to a string. So I'll have to take a look at why the Handson table is behaving this way. — Jaime
– Jaime, Commented Nov 7, 2015 at 15:07

Jaime · Accepted Answer · 2015-12-01 03:19:15Z

My issue turned out to be the default settings for handsontable. while I was supplying the table with float values, by default, the table was converting them to strings. so I was posting a matrix of strings that looked like float. the fix was simply to reformat the handsontable cells where the data was placed.

var data = function () {
   return Handsontable.helper.createSpreadsheetData(mtxrows, mtxcols);
  };

  var hot = new Handsontable(container, {
    data: data,
    height: 480,
    colHeaders: true,
    rowHeaders: true,
    stretchH: 'none',
    columnSorting: true,
    contextMenu: true,
    className: "htCenter",
    cells: function (row, col, prop) {
        var cellProperties = {};
        if (row > 0) {
          cellProperties.type = 'numeric';
          cellProperties.format = '0[.]000';
         }                      
        return cellProperties;
        },

    afterChange: function () {
        var tmpData = JSON.parse(JSON.stringify(mtx_data));
    }
  });

So basically anything after the first row is set to numeric type.

so now this line in my ajax call:

dsg_mtx : JSON.stringify(dsg_mtx),

formats it correctly and views.py uses this call to load it in properly:

designMtx = json.loads(request.POST['dsg_mtx'])

Thanks to Tomasz Jakub for suggesting the console.log() which helped me diagnose the issue.

Regards, Jaime

levi · Accepted Answer · 2015-11-06 06:48:27Z

0

Try json.loads but in parse_float pass decimal.Decimal

designMtx = json.loads(request.POST['dsg_mtx'], parse_float=decimal.Decimal)

answered Nov 6, 2015 at 6:48

levi

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1 Comment

Jaime Over a year ago

Tried it, but it says that decimal is not defined. after adding: from decimal import Decimal and changing the code to: ... parse_float=Decimal the code runs, but has no impact on the outcome. designMtx is still just a string.

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