Embedding layer w/ mask in a nested model

[jpraymond]

The following code raises an error on the last line (when attempting to fit the model). However it works fine if mask_zero is set to False. It also works if base_model is added to a Sequential model.

import numpy as np

from keras.models import Model
from keras.layers import Input, Embedding, SimpleRNN, Dense


# Base model
base_inputs = Input(shape=(10, ))
embeddings = Embedding(input_dim=100,
                       output_dim=16,
                       mask_zero=True)(base_inputs)
base_out = SimpleRNN(32)(embeddings)
base_model = Model(base_inputs, base_out)

# Using the base model in another model, with the Functional API.
inputs = Input(shape=(10, ))
processed_inputs = base_model(inputs)
out = Dense(1)(processed_inputs)

model = Model(inputs, out)
model.compile(loss='mse', optimizer='rmsprop')

x = np.random.randint(0, 100, (1000, 10))
y = np.random.rand(1000)

model.fit(x, y, epochs=10)

Traceback using Tensorflow:

Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/tensorflow/python/client/session.py", line 1022, in _do_call
    return fn(*args)
  File "/usr/local/lib/python3.6/site-packages/tensorflow/python/client/session.py", line 1004, in _run_fn
    status, run_metadata)
  File "/usr/local/Cellar/python3/3.6.0_1/Frameworks/Python.framework/Versions/3.6/lib/python3.6/contextlib.py", line 89, in __exit__
    next(self.gen)
  File "/usr/local/lib/python3.6/site-packages/tensorflow/python/framework/errors_impl.py", line 469, in raise_exception_on_not_ok_status
    pywrap_tensorflow.TF_GetCode(status))
tensorflow.python.framework.errors_impl.InvalidArgumentError: You must feed a value for placeholder tensor 'input_1' with dtype float
	 [[Node: input_1 = Placeholder[dtype=DT_FLOAT, shape=[], _device="/job:localhost/replica:0/task:0/cpu:0"]()]]

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "temp.py", line 26, in <module>
    model.fit(x, y, epochs=10)
  File "/usr/local/lib/python3.6/site-packages/keras/engine/training.py", line 1486, in fit
    initial_epoch=initial_epoch)
  File "/usr/local/lib/python3.6/site-packages/keras/engine/training.py", line 1141, in _fit_loop
    outs = f(ins_batch)
  File "/usr/local/lib/python3.6/site-packages/keras/backend/tensorflow_backend.py", line 2102, in __call__
    feed_dict=feed_dict)
  File "/usr/local/lib/python3.6/site-packages/tensorflow/python/client/session.py", line 767, in run
    run_metadata_ptr)
  File "/usr/local/lib/python3.6/site-packages/tensorflow/python/client/session.py", line 965, in _run
    feed_dict_string, options, run_metadata)
  File "/usr/local/lib/python3.6/site-packages/tensorflow/python/client/session.py", line 1015, in _do_run
    target_list, options, run_metadata)
  File "/usr/local/lib/python3.6/site-packages/tensorflow/python/client/session.py", line 1035, in _do_call
    raise type(e)(node_def, op, message)
tensorflow.python.framework.errors_impl.InvalidArgumentError: You must feed a value for placeholder tensor 'input_1' with dtype float
	 [[Node: input_1 = Placeholder[dtype=DT_FLOAT, shape=[], _device="/job:localhost/replica:0/task:0/cpu:0"]()]]

Caused by op 'input_1', defined at:
  File "temp.py", line 8, in <module>
    base_inputs = Input(shape=(10, ))
  File "/usr/local/lib/python3.6/site-packages/keras/engine/topology.py", line 1391, in Input
    input_tensor=tensor)
  File "/usr/local/lib/python3.6/site-packages/keras/engine/topology.py", line 1302, in __init__
    name=self.name)
  File "/usr/local/lib/python3.6/site-packages/keras/backend/tensorflow_backend.py", line 350, in placeholder
    x = tf.placeholder(dtype, shape=shape, name=name)
  File "/usr/local/lib/python3.6/site-packages/tensorflow/python/ops/array_ops.py", line 1520, in placeholder
    name=name)
  File "/usr/local/lib/python3.6/site-packages/tensorflow/python/ops/gen_array_ops.py", line 2149, in _placeholder
    name=name)
  File "/usr/local/lib/python3.6/site-packages/tensorflow/python/framework/op_def_library.py", line 763, in apply_op
    op_def=op_def)
  File "/usr/local/lib/python3.6/site-packages/tensorflow/python/framework/ops.py", line 2395, in create_op
    original_op=self._default_original_op, op_def=op_def)
  File "/usr/local/lib/python3.6/site-packages/tensorflow/python/framework/ops.py", line 1264, in __init__
    self._traceback = _extract_stack()

InvalidArgumentError (see above for traceback): You must feed a value for placeholder tensor 'input_1' with dtype float
	 [[Node: input_1 = Placeholder[dtype=DT_FLOAT, shape=[], _device="/job:localhost/replica:0/task:0/cpu:0"]()]]

Traceback using Theano:

Traceback (most recent call last):
  File "temp.py", line 26, in <module>
    model.fit(x, y, epochs=10)
  File "/usr/local/lib/python3.6/site-packages/keras/engine/training.py", line 1458, in fit
    self._make_train_function()
  File "/usr/local/lib/python3.6/site-packages/keras/engine/training.py", line 1008, in _make_train_function
    **self._function_kwargs)
  File "/usr/local/lib/python3.6/site-packages/keras/backend/theano_backend.py", line 1132, in function
    return Function(inputs, outputs, updates=updates, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/keras/backend/theano_backend.py", line 1118, in __init__
    **kwargs)
  File "/usr/local/lib/python3.6/site-packages/theano/compile/function.py", line 326, in function
    output_keys=output_keys)
  File "/usr/local/lib/python3.6/site-packages/theano/compile/pfunc.py", line 486, in pfunc
    output_keys=output_keys)
  File "/usr/local/lib/python3.6/site-packages/theano/compile/function_module.py", line 1808, in orig_function
    output_keys=output_keys).create(
  File "/usr/local/lib/python3.6/site-packages/theano/compile/function_module.py", line 1446, in __init__
    accept_inplace)
  File "/usr/local/lib/python3.6/site-packages/theano/compile/function_module.py", line 177, in std_fgraph
    update_mapping=update_mapping)
  File "/usr/local/lib/python3.6/site-packages/theano/gof/fg.py", line 174, in __init__
    self.__import_r__(output, reason="init")
  File "/usr/local/lib/python3.6/site-packages/theano/gof/fg.py", line 345, in __import_r__
    self.__import__(variable.owner, reason=reason)
  File "/usr/local/lib/python3.6/site-packages/theano/gof/fg.py", line 390, in __import__
    raise MissingInputError(error_msg, variable=r)
theano.gof.fg.MissingInputError: Input 0 of the graph (indices start from 0), used to compute Elemwise{neq,no_inplace}(/input_1, InplaceDimShuffle{x,x}.0), was not provided and not given a value. Use the Theano flag exception_verbosity='high', for more information on this error.
 
Backtrace when that variable is created:

  File "temp.py", line 8, in <module>
    base_inputs = Input(shape=(10, ))
  File "/usr/local/lib/python3.6/site-packages/keras/engine/topology.py", line 1391, in Input
    input_tensor=tensor)
  File "/usr/local/lib/python3.6/site-packages/keras/engine/topology.py", line 1302, in __init__
    name=self.name)
  File "/usr/local/lib/python3.6/site-packages/keras/backend/theano_backend.py", line 184, in placeholder
    x = T.TensorType(dtype, broadcast)(name)

OS: Mac OS X
Keras: 2.0.2
Tensorflow (cpu): 1.0.0
Theano: 0.9.0

[fchollet]

Fix at master.