Returns (at runtime) the absolute path of the input DKK file.

def ddk_filepath(self):
        """Returns (at runtime) the absolute path of the input DKK file."""
        if self.ddk_node is None: return "DDK_FILE_DOES_NOT_EXIST"
        if isinstance(self.ddk_node, FileNode): return self.ddk_node.filepath

        path = self.ddk_node.outdir.has_abiext("DDK")
        return path if path else "DDK_FILE_DOES_NOT_EXIST"