Keras error "You must feed a value for placeholder tensor 'bidirectional_1/keras_learning_phase' with dtype bool"

Question

I get the following error for the code snippet below:

You must feed a value for placeholder tensor 'bidirectional_1/keras_learning_phase' with dtype bool

If I add the dropout layer model.add(Dropout(dropout)), it works. Anyone knows why? The back-end is Tensorflow, Keras 2.0.1

def prep_model1(embedding_layer1, embedding_layer2, dropout=0.5):

    model0 = Sequential()  
    model0.add(embedding_layer1)
    model0.add(Bidirectional(LSTM(128, return_sequences=False, dropout=dropout)))

    model1 = Sequential() 
    model1.add(embedding_layer2)
    model1.add(Bidirectional(LSTM(128, return_sequences=False, dropout=dropout)))

    model = Sequential()
    model.add(Merge([model0, model1], mode='concat', concat_axis=1))
    #model.add(Dropout(dropout))
    model.add(Dense(1, activation='sigmoid'))

    return model

Answer 1

Try to import K and set learning phase before your model.

from keras import backend as K

K.set_learning_phase(1) #set learning phase

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