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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_enabled_features(self, user_id, attributes=None):
 """ Returns the list of features that are enabled for the user. Args: user_id: ID for user. attributes: Dict representing user attributes. Returns: A list of the keys of the features that are enabled for the user. """


    enabled_features = []
    if not self.is_valid:
      self.logger.error(enums.Errors.INVALID_DATAFILE.format('get_enabled_features'))
      return enabled_features

    if not isinstance(user_id, string_types):
      self.logger.error(enums.Errors.INVALID_INPUT_ERROR.format('user_id'))
      return enabled_features

    if not self._validate_user_inputs(attributes):
      return enabled_features

    for feature in self.config.feature_key_map.values():
      if self.is_feature_enabled(feature.key, user_id, attributes):
        enabled_features.append(feature.key)

    return enabled_features