code: def posted_data(self, field):
          
          try:
              return self.cleaned_data[field]
          except (AttributeError, KeyError):
              return field.endswith("_export")
docs: Wrapper for self.cleaned_data that returns True on
          field_id_export fields when the form hasn't been posted to,
          to facilitate show/export URLs that export all entries without
          a form submission.