TypeError: Could not locate class 'adam'. Make sure custom classes are decorated with `@keras.saving.register_keras_serializable()`

[mpetteno]

Hi everyone,

I think there is a problem with the loading of a model that has been compiled providing the optimizer as a dict.
This does not happen if optimizer="adam" or optimizer=keras.optimizers.Adam()

Here the code that reproduces the issue:

model = keras.models.Sequential()
model.add(keras.layers.Dense(64, input_dim=3, activation='relu'))
model.add(keras.layers.Dense(32, activation='relu'))
model.add(keras.layers.Dense(1, activation='linear'))

model.compile(
    optimizer={
      "class_name": "Adam",
      "config": {
        "learning_rate": 0.01,
        "beta_1": 0.9,
        "beta_2": 0.999,
        "epsilon": 1e-7
      }
    },
    loss='mse'
)

keras.saving.save_model(model, 'model.keras')
loaded_model = keras.saving.load_model("model.keras")

The full traceback is:

Traceback (most recent call last):
File "/venv/lib/python3.11/site-packages/keras/src/saving/saving_lib.py", line 152, in load_model
return _load_model_from_fileobj(
^^^^^^^^^^^^^^^^^^^^^^^^^
File "/venv/lib/python3.11/site-packages/keras/src/saving/saving_lib.py", line 170, in _load_model_from_fileobj
model = deserialize_keras_object(
^^^^^^^^^^^^^^^^^^^^^^^^^
File "/venv/lib/python3.11/site-packages/keras/src/saving/serialization_lib.py", line 734, in deserialize_keras_object
instance.compile_from_config(compile_config)
File "/venv/lib/python3.11/site-packages/keras/src/trainers/trainer.py", line 870, in compile_from_config
config = serialization_lib.deserialize_keras_object(config)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/venv/lib/python3.11/site-packages/keras/src/saving/serialization_lib.py", line 594, in deserialize_keras_object
return {
^
File "/venv/lib/python3.11/site-packages/keras/src/saving/serialization_lib.py", line 595, in
key: deserialize_keras_object(
^^^^^^^^^^^^^^^^^^^^^^^^^
File "/venv/lib/python3.11/site-packages/keras/src/saving/serialization_lib.py", line 694, in deserialize_keras_object
cls = _retrieve_class_or_fn(
^^^^^^^^^^^^^^^^^^^^^^
File "/venv/lib/python3.11/site-packages/keras/src/saving/serialization_lib.py", line 812, in _retrieve_class_or_fn
raise TypeError(
TypeError: Could not locate class 'adam'. Make sure custom classes are decorated with @keras.saving.register_keras_serializable(). Full object config: {'class_name': 'adam', 'config': {'learning_rate': 0.01, 'beta_1': 0.9, 'beta_2': 0.999, 'epsilon': 1e-07}}

I think that this is due to the fact that in this case the class_name field is serialized as "adam" (lowe case) and not "Adam" (capitalized) and thus in serialization_lib.py at line 803 obj is no resolved.

Thanks for your help.

[fchollet]

Thanks for the report, this is fixed at HEAD. Note that passing optimizers as dicts isn't an officially supported API (officially supported APIs are to pass it as a string or as an Optimizer instance).