code: def default_loader(obj, defaults=None):
      
      defaults = defaults or {}
      default_settings_values = {
          key: value
          for key, value in default_settings.__dict__.items()  # noqa
          if key.isupper()
      }
  
      all_keys = deduplicate(
          list(defaults.keys()) + list(default_settings_values.keys())
      )
  
      for key in all_keys:
          if not obj.exists(key):
              value = defaults.get(key, default_settings_values.get(key))
              obj.logger.debug("loading: %s:%s", key, value)
              obj.set(key, value)
  
      # start dotenv to get default env vars from there
      # check overrides in env vars
      default_settings.start_dotenv(obj)
  
      # Deal with cases where a custom ENV_SWITCHER_IS_PROVIDED
      # Example: Flask and Django Extensions
      env_switcher = defaults.get(
          "ENV_SWITCHER_FOR_DYNACONF", "ENV_FOR_DYNACONF"
      )
  
      for key in all_keys:
          if key not in default_settings_values.keys():
              continue
  
          env_value = obj.get_environ(
              env_switcher if key == "ENV_FOR_DYNACONF" else key,
              default="_not_found",
          )
  
          if env_value != "_not_found":
              obj.logger.debug("overriding from envvar: %s:%s", key, env_value)
              obj.set(key, env_value, tomlfy=True)
docs: Loads default settings and check if there are overridings
      exported as environment variables