def internal_files(self):
        """Return a list of the intermediate files produced by this link.

        This returns all files that were explicitly marked as internal files.
        """
        ret_list = []
        for key, val in self.file_dict.items():
            # For internal files we only want files that were marked as
            # internal
            if val & FileFlags.internal_mask:
                ret_list.append(key)
        return ret_list
Return a list of the intermediate files produced by this link.

        This returns all files that were explicitly marked as internal files.