h5 to dict and back does not return same file

[ajroeth205]

There seems to be an issue where when converting an H5 file to a dictionary and back using h5_to_dict and dict_to_h5, the H5 file is no longer the same as the original. This happens when an attribute, in this case weight_names, has an empty field, in this case called values. This is the case for dropout layers in Keras models, so you can reproduce the error using a keras model with a dropout layer.

Minimum reproducible example:

from tensorflow import keras
import h5_to_json as h5j

def demo_issue(dropout: bool):
    model = keras.Sequential()

    model.add(keras.layers.LSTM(
        units=2,
        input_shape=(1,1)
    ))

    if dropout:
        model.add(keras.layers.Dropout(0.2))

    model.add(keras.layers.Dense(units=1))

    model.compile(
        loss='mean_squared_error',
        optimizer=keras.optimizers.Adam(0.001)
    )

    model.save('./model.h5')

    # This succeeds
    immediate_reloaded_model = keras.models.load_model('./model.h5')

    model_dict = h5j.h5_to_dict('./model.h5', include_datasets=True)

    h5j.dict_to_h5(model_dict, './model.h5')

    # This fails if the model has a dropout layer
    dict_stored_model = keras.models.load_model('./model.h5')

print("Without dropout layer:")
demo_issue(False)
print("With dropout layer:")
demo_issue(True)

The warning given by h5_to_dict is:

no value key in attribute: weight_names

The error this causes when running keras.models.load_model is:

Traceback (most recent call last):
  File "/Users/javieralcazar/Javier/MYAPPS/anaconda3/lib/python3.7/site-packages/tensorflow_core/python/keras/saving/hdf5_format.py", line 171, in load_model_from_hdf5
    load_weights_from_hdf5_group(f['model_weights'], model.layers)
  File "/Users/javieralcazar/Javier/MYAPPS/anaconda3/lib/python3.7/site-packages/tensorflow_core/python/keras/saving/hdf5_format.py", line 669, in load_weights_from_hdf5_group
    weight_names = load_attributes_from_hdf5_group(g, 'weight_names')
  File "/Users/javieralcazar/Javier/MYAPPS/anaconda3/lib/python3.7/site-packages/tensorflow_core/python/keras/saving/hdf5_format.py", line 842, in load_attributes_from_hdf5_group
    data = [n.decode('utf8') for n in group.attrs[name]]
TypeError: 'Empty' object is not iterable

How can we convert this H5 file to a dict and back and get the same H5 file back? I believe this would mean having an empty values field in the weight_names attribute rather than erasing the values field completely. Thank you.