🐛 Bug

Information

I am trying to build a Keras Sequential model, where, I use DistillBERT as a non-trainable embedding layer. The model complies and fits well, even predict method works. But when I want to save it using model.save(model.h5), It fails and shows the following error:

> ---------------------------------------------------------------------------
> NotImplementedError                       Traceback (most recent call last)
> <ipython-input-269-557c9cec7497> in <module>
> ----> 1 model.get_config()
> 
> /usr/local/lib/python3.7/site-packages/tensorflow/python/keras/engine/network.py in get_config(self)
>     966     if not self._is_graph_network:
>     967       raise NotImplementedError
> --> 968     return copy.deepcopy(get_network_config(self))
>     969 
>     970   @classmethod
> 
> /usr/local/lib/python3.7/site-packages/tensorflow/python/keras/engine/network.py in get_network_config(network, serialize_layer_fn)
>    2117           filtered_inbound_nodes.append(node_data)
>    2118 
> -> 2119     layer_config = serialize_layer_fn(layer)
>    2120     layer_config['name'] = layer.name
>    2121     layer_config['inbound_nodes'] = filtered_inbound_nodes
> 
> /usr/local/lib/python3.7/site-packages/tensorflow/python/keras/utils/generic_utils.py in serialize_keras_object(instance)
>     273         return serialize_keras_class_and_config(
>     274             name, {_LAYER_UNDEFINED_CONFIG_KEY: True})
> --> 275       raise e
>     276     serialization_config = {}
>     277     for key, item in config.items():
> 
> /usr/local/lib/python3.7/site-packages/tensorflow/python/keras/utils/generic_utils.py in serialize_keras_object(instance)
>     268     name = get_registered_name(instance.__class__)
>     269     try:
> --> 270       config = instance.get_config()
>     271     except NotImplementedError as e:
>     272       if _SKIP_FAILED_SERIALIZATION:
> 
> /usr/local/lib/python3.7/site-packages/tensorflow/python/keras/engine/network.py in get_config(self)
>     965   def get_config(self):
>     966     if not self._is_graph_network:
> --> 967       raise NotImplementedError
>     968     return copy.deepcopy(get_network_config(self))
>     969 
> 
> NotImplementedError: 

The language I am using the model in English.

The problem arises when using my own modified scripts: (give details below)

from transformers import DistilBertConfig, TFDistilBertModel, DistilBertTokenizer
max_len = 8
distil_bert = 'distilbert-base-uncased'
config = DistilBertConfig(dropout=0.2, attention_dropout=0.2)
config.output_hidden_states = False
transformer_model = TFDistilBertModel.from_pretrained(distil_bert, config = config)

input_word_ids = tf.keras.layers.Input(shape=(max_len,), dtype = tf.int32, name = "input_word_ids")
distill_output =  transformer_model(input_word_ids)[0]

cls_out = tf.keras.layers.Lambda(lambda seq: seq[:, 0, :])(distill_output)
X = tf.keras.layers.BatchNormalization()(cls_out)
X = tf.keras.layers.Dense(256, activation='relu')(X)
X = tf.keras.layers.Dropout(0.2)(X)

X = tf.keras.layers.BatchNormalization()(X)
X = tf.keras.layers.Dense(128, activation='relu')(X)
X = tf.keras.layers.Dropout(0.2)(X)

X = tf.keras.layers.BatchNormalization()(X)
X = tf.keras.layers.Dense(64, activation='relu')(X)
X = tf.keras.layers.Dropout(0.2)(X)

X = tf.keras.layers.Dense(2)(X)
model = tf.keras.Model(inputs=input_word_ids, outputs=X)

for layer in model.layers[:3]:
    layer.trainable = False

The tasks I am working on is my own dataset.

To reproduce

Steps to reproduce the behavior:

1. Run the above code
2. You will get the error when saving the model as

model.save('model.h5')

You can get the same error if you try:

model.get_config()

An interesting observation: if you save the model without specifying “.h5” like

model.save('./model')

it saves the model as TensorFlow saved_model format and creates folders (assets (empty), variables, and some index files). But if you try to load the model, it produces different errors related to the DistillBert/Bert. It may be due to some naming inconsistency (input_ids vs. inputs, see below) inside the DistillBert model.

new_model = tf.keras.models.load_model('./model)

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
/usr/local/lib/python3.7/site-packages/tensorflow/python/util/nest.py in assert_same_structure(nest1, nest2, check_types, expand_composites)
    377     _pywrap_utils.AssertSameStructure(nest1, nest2, check_types,
--> 378                                       expand_composites)
    379   except (ValueError, TypeError) as e:

ValueError: The two structures don't have the same nested structure.

First structure: type=dict str={'input_ids': TensorSpec(shape=(None, 5), dtype=tf.int32, name='input_ids')}

Second structure: type=TensorSpec str=TensorSpec(shape=(None, 8), dtype=tf.int32, name='inputs')

More specifically: Substructure "type=dict str={'input_ids': TensorSpec(shape=(None, 5), dtype=tf.int32, name='input_ids')}" is a sequence, while substructure "type=TensorSpec str=TensorSpec(shape=(None, 8), dtype=tf.int32, name='inputs')" is not

During handling of the above exception, another exception occurred:

ValueError                                Traceback (most recent call last)
<ipython-input-229-b46ed71fd9ad> in <module>
----> 1 new_model = tf.keras.models.load_model(keras_model_path)

/usr/local/lib/python3.7/site-packages/tensorflow/python/keras/saving/save.py in load_model(filepath, custom_objects, compile)
    188     if isinstance(filepath, six.string_types):
    189       loader_impl.parse_saved_model(filepath)
--> 190       return saved_model_load.load(filepath, compile)
    191 
    192   raise IOError(

/usr/local/lib/python3.7/site-packages/tensorflow/python/keras/saving/saved_model/load.py in load(path, compile)
    114   # TODO(kathywu): Add saving/loading of optimizer, compiled losses and metrics.
    115   # TODO(kathywu): Add code to load from objects that contain all endpoints
--> 116   model = tf_load.load_internal(path, loader_cls=KerasObjectLoader)
    117 
    118   # pylint: disable=protected-access

/usr/local/lib/python3.7/site-packages/tensorflow/python/saved_model/load.py in load_internal(export_dir, tags, loader_cls)
    602       loader = loader_cls(object_graph_proto,
    603                           saved_model_proto,
--> 604                           export_dir)
    605       root = loader.get(0)
    606       if isinstance(loader, Loader):

/usr/local/lib/python3.7/site-packages/tensorflow/python/keras/saving/saved_model/load.py in __init__(self, *args, **kwargs)
    186     self._models_to_reconstruct = []
    187 
--> 188     super(KerasObjectLoader, self).__init__(*args, **kwargs)
    189 
    190     # Now that the node object has been fully loaded, and the checkpoint has

/usr/local/lib/python3.7/site-packages/tensorflow/python/saved_model/load.py in __init__(self, object_graph_proto, saved_model_proto, export_dir)
    121       self._concrete_functions[name] = _WrapperFunction(concrete_function)
    122 
--> 123     self._load_all()
    124     self._restore_checkpoint()
    125 

/usr/local/lib/python3.7/site-packages/tensorflow/python/keras/saving/saved_model/load.py in _load_all(self)
    213 
    214     # Finish setting up layers and models. See function docstring for more info.
--> 215     self._finalize_objects()
    216 
    217   @property

/usr/local/lib/python3.7/site-packages/tensorflow/python/keras/saving/saved_model/load.py in _finalize_objects(self)
    504         layers_revived_from_saved_model.append(node)
    505 
--> 506     _finalize_saved_model_layers(layers_revived_from_saved_model)
    507     _finalize_config_layers(layers_revived_from_config)
    508 

/usr/local/lib/python3.7/site-packages/tensorflow/python/keras/saving/saved_model/load.py in _finalize_saved_model_layers(layers)
    675       call_fn = _get_keras_attr(layer).call_and_return_conditional_losses
    676       if call_fn.input_signature is None:
--> 677         inputs = infer_inputs_from_restored_call_function(call_fn)
    678       else:
    679         inputs = call_fn.input_signature[0]

/usr/local/lib/python3.7/site-packages/tensorflow/python/keras/saving/saved_model/load.py in infer_inputs_from_restored_call_function(fn)
    919   for concrete in fn.concrete_functions[1:]:
    920     spec2 = concrete.structured_input_signature[0][0]
--> 921     spec = nest.map_structure(common_spec, spec, spec2)
    922   return spec
    923 

/usr/local/lib/python3.7/site-packages/tensorflow/python/util/nest.py in map_structure(func, *structure, **kwargs)
    609   for other in structure[1:]:
    610     assert_same_structure(structure[0], other, check_types=check_types,
--> 611                           expand_composites=expand_composites)
    612 
    613   flat_structure = [flatten(s, expand_composites) for s in structure]

/usr/local/lib/python3.7/site-packages/tensorflow/python/util/nest.py in assert_same_structure(nest1, nest2, check_types, expand_composites)
    383                   "Entire first structure:\n%s\n"
    384                   "Entire second structure:\n%s"
--> 385                   % (str(e), str1, str2))
    386 
    387 

ValueError: The two structures don't have the same nested structure.

First structure: type=dict str={'input_ids': TensorSpec(shape=(None, 5), dtype=tf.int32, name='input_ids')}

Second structure: type=TensorSpec str=TensorSpec(shape=(None, 8), dtype=tf.int32, name='inputs')

More specifically: Substructure "type=dict str={'input_ids': TensorSpec(shape=(None, 5), dtype=tf.int32, name='input_ids')}" is a sequence, while substructure "type=TensorSpec str=TensorSpec(shape=(None, 8), dtype=tf.int32, name='inputs')" is not
Entire first structure:
{'input_ids': .}
Entire second structure:
.

Expected behavior

I expect to have a normal saving and loading of the model.

Environment info

• transformers version: 2.9.1
• Platform:
• Python version: 3.7.6
• Tensorflow version (CPU): 2.2.0
• Using GPU in script?: No
• Using distributed or parallel set-up in script?: No