code: def _prepare_wsdl_objects(self):
          
  
          self.SelectionDetails = self.client.factory.create('TrackSelectionDetail')
  
          # Default to Fedex
          self.SelectionDetails.CarrierCode = 'FDXE'
  
          track_package_id = self.client.factory.create('TrackPackageIdentifier')
  
          # Default to tracking number.
          track_package_id.Type = 'TRACKING_NUMBER_OR_DOORTAG'
  
          self.SelectionDetails.PackageIdentifier = track_package_id
docs: This sets the package identifier information. This may be a tracking
          number or a few different things as per the Fedex spec.