keras/src/export/export_lib.py/ExportArchive/__init__
class ExportArchive:    def __init__(self):
        self._endpoint_names = []
        self._endpoint_signatures = {}
        self.tensorflow_version = tf.__version__

        self._tf_trackable = tf.__internal__.tracking.AutoTrackable()
        self._tf_trackable.variables = []
        self._tf_trackable.trainable_variables = []
        self._tf_trackable.non_trainable_variables = []

        if backend.backend() == "jax":
            self._backend_variables = []
            self._backend_trainable_variables = []
            self._backend_non_trainable_variables = []

        if backend.backend() not in ("tensorflow", "jax"):
            raise NotImplementedError(
                "The export API is only compatible with JAX and TF backends."
            )