Key Code Blocks of Keras LSTM Dropout Implementation

lstm_recurrent_dropout.py

# https://github.com/tensorflow/tensorflow/blob/v1.3.0/tensorflow/contrib/keras/python/keras/layers/recurrent.py#L1174
class LSTM(Recurrent):
  #...
  def get_constants(self, inputs, training=None):
    #...
    ones = K.ones_like(K.reshape(inputs[:, 0, 0], (-1, 1)))
    ones = K.tile(ones, (1, self.units))
    def dropped_inputs():  # pylint: disable=function-redefined
      return K.dropout(ones, self.recurrent_dropout)
    rec_dp_mask = [
        K.in_train_phase(dropped_inputs, ones, training=training)
        for _ in range(4)
    ]
#...