code: def install_dir(self):
          
          max_len = 500
  
          directory = self._get_str(self._iface.get_install_dir, [self.app_id], max_len=max_len)
  
          if not directory:
              # Fallback to restricted interface (can only be used by approved apps).
              directory = self._get_str(self._iface_list.get_install_dir, [self.app_id], max_len=max_len)
  
          return directory
docs: Returns application installation path.
  
          .. note::
  
              If fails this falls back to a restricted interface, which can only be used by approved apps.
  
          :rtype: str