Compatible with Py38 (#351)

keras_core/layers/layer.py

@@ -1021,7 +1021,7 @@ class Layer(BackendLayer, Operation):
             # Case: all input keyword arguments were plain tensors.
             input_tensors = {
                 # We strip the `_shape` suffix to recover kwarg names.
-                k.removesuffix("_shape"): backend.KerasTensor(shape)
+                utils.removesuffix(k, "_shape"): backend.KerasTensor(shape)
                 for k, shape in shapes_dict.items()
             }
             try:
@@ -1286,7 +1286,7 @@ def check_shapes_signature(target_fn, call_spec, cls):
                 f"Received `{method_name}()` argument "
                 f"`{name}`, which does not end in `_shape`."
             )
-        expected_call_arg = name.removesuffix("_shape")
+        expected_call_arg = utils.removesuffix(name, "_shape")
         if expected_call_arg not in call_spec.arguments_dict:
             raise ValueError(
                 f"{error_preamble} For layer '{cls.__name__}', "

keras_core/layers/rnn/bidirectional.py

@@ -1,6 +1,7 @@
 import copy
 
 from keras_core import operations as ops
+from keras_core import utils
 from keras_core.api_export import keras_core_export
 from keras_core.layers.core.wrapper import Wrapper
 from keras_core.layers.layer import Layer
@@ -109,16 +110,16 @@ class Bidirectional(Wrapper):
         # Recreate the forward layer from the original layer config, so that it
         # will not carry over any state from the layer.
         config = serialization_lib.serialize_keras_object(layer)
-        config["config"]["name"] = "forward_" + layer.name.removeprefix(
-            "forward_"
+        config["config"]["name"] = "forward_" + utils.removeprefix(
+            layer.name, "forward_"
         )
         self.forward_layer = serialization_lib.deserialize_keras_object(config)
 
         if backward_layer is None:
             config = serialization_lib.serialize_keras_object(layer)
             config["config"]["go_backwards"] = True
-            config["config"]["name"] = "backward_" + layer.name.removeprefix(
-                "backward_"
+            config["config"]["name"] = "backward_" + utils.removeprefix(
+                layer.name, "backward_"
             )
             self.backward_layer = serialization_lib.deserialize_keras_object(
                 config

keras_core/testing/test_case.py

@@ -8,6 +8,7 @@ from tensorflow import nest
 
 from keras_core import backend
 from keras_core import operations as ops
+from keras_core import utils
 from keras_core.models import Model
 from keras_core.utils import traceback_utils
 
@@ -336,7 +337,9 @@ def create_keras_tensors(input_shape, dtype):
         return [keras_tensor.KerasTensor(s, dtype=dtype) for s in input_shape]
     if isinstance(input_shape, dict):
         return {
-            k.removesuffix("_shape"): keras_tensor.KerasTensor(v, dtype=dtype)
+            utils.removesuffix(k, "_shape"): keras_tensor.KerasTensor(
+                v, dtype=dtype
+            )
             for k, v in input_shape.items()
         }
 
@@ -370,6 +373,6 @@ def create_eager_tensors(input_shape, dtype):
         return [create_fn(s, dtype=dtype) for s in input_shape]
     if isinstance(input_shape, dict):
         return {
-            k.removesuffix("_shape"): create_fn(v, dtype=dtype)
+            utils.removesuffix(k, "_shape"): create_fn(v, dtype=dtype)
             for k, v in input_shape.items()
         }

keras_core/utils/__init__.py

@@ -18,5 +18,7 @@ from keras_core.utils.numerical_utils import to_categorical
 from keras_core.utils.progbar import Progbar
 from keras_core.utils.python_utils import default
 from keras_core.utils.python_utils import is_default
+from keras_core.utils.python_utils import removeprefix
+from keras_core.utils.python_utils import removesuffix
 from keras_core.utils.rng_utils import set_random_seed
 from keras_core.utils.sequence_utils import pad_sequences

keras_core/utils/python_utils.py

@@ -122,3 +122,21 @@ def remove_long_seq(maxlen, seq, label):
             new_seq.append(x)
             new_label.append(y)
     return new_seq, new_label
+
+
+def removeprefix(x, prefix):
+    """Backport of `removeprefix` from PEP-616 (Python 3.9+)"""
+
+    if len(prefix) > 0 and x.startswith(prefix):
+        return x[len(prefix) :]
+    else:
+        return x
+
+
+def removesuffix(x, suffix):
+    """Backport of `removesuffix` from PEP-616 (Python 3.9+)"""
+
+    if len(suffix) > 0 and x.endswith(suffix):
+        return x[: -len(suffix)]
+    else:
+        return x

keras_core/utils/python_utils_test.py

@@ -10,3 +10,13 @@ class PythonUtilsTest(testing.TestCase):
         serialized = python_utils.func_dump(my_function)
         deserialized = python_utils.func_load(serialized)
         self.assertEqual(deserialized(2, y=3), 5)
+
+    def test_removesuffix(self):
+        x = "model.keras"
+        self.assertEqual(python_utils.removesuffix(x, ".keras"), "model")
+        self.assertEqual(python_utils.removesuffix(x, "model"), x)
+
+    def test_removeprefix(self):
+        x = "model.keras"
+        self.assertEqual(python_utils.removeprefix(x, "model"), ".keras")
+        self.assertEqual(python_utils.removeprefix(x, ".keras"), x)