code: def load_user_envs(self):
          
          installed_packages = self._list_packages()
  
          # Tagging core envs
          gym_package = 'gym ({})'.format(installed_packages['gym']) if 'gym' in installed_packages else 'gym'
          core_specs = registry.all()
          for spec in core_specs:
              spec.source = 'OpenAI Gym Core Package'
              spec.package = gym_package
  
          # Loading user envs
          if not os.path.isfile(self.cache_path):
              return
          with open(self.cache_path) as cache:
              for line in cache:
                  user_package, registered_envs = self._load_package(line.rstrip('\n'), installed_packages)
                  if logger.level <= logging.DEBUG:
                      logger.debug('Installed %d user environments from package "%s"', len(registered_envs), user_package['name'])
          if self.cache_needs_update:
              self._update_cache()
          if len(self.env_ids) > 0:
              logger.info('Found and registered %d user environments.', len(self.env_ids))
docs: Loads downloaded user envs from filesystem cache on `import gym`