code: def _lookup_used_entity_id(self, file_details):
          
          # Since this uses the response from POST to /files/ this will include the ancestors and not be
          # effected by exclude_response_fields that were used when listing the project
          name_parts = [ancestor['name'] for ancestor in file_details['ancestors']
                        if ancestor['kind'] == KindType.folder_str]
          name_parts.append(file_details['name'])
          remote_path = os.sep.join(name_parts)
          return self.activity.remote_path_to_file_version_id[remote_path]
docs: Return the file_version_id associated with the path from file_details.
          The file_version_id is looked up from a dictionary in the activity.
          :param file_details: dict: response from DukeDS POST to /files/
          :return: str: file_version_id uuid