gistfile1.js

// https://example.com/index.html
$('#fileupload').fileupload({
  url: 'https://apiexample.com/upload/image/',
  dataType: 'text',
  paramName: 'file',
  redirect: 'https://example.com/result.html?%s',

  add: function (event, data) {
    // Start upload
    data.submit();
  },

  done: function (event, data) {
    // Successful upload. Parse JSON text response
    var result = $.parseJSON(data.result);
  },

  fail: function (event, data) {
    // Failed upload
  }
});

gistfile2.py

def post(self):
    if (self.request.get('_method') == 'DELETE'):
        return self.delete()
    result = {'files': self.handle_upload()}
    s = json.dumps(result, separators=(',', ':'))
    redirect = self.request.get('redirect')
    if redirect:
        return self.redirect(str(
            redirect.replace('%s', urllib.quote(s, ''), 1)
        ))
    if 'application/json' in self.request.headers.get('Accept'):
        self.response.headers['Content-Type'] = 'application/json'
    self.response.write(s)