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import mxnet as mx
from mxnet import gluon
from mxnet.gluon import nn, rnn

class RNNModel(gluon.Block):
    """A model with an encoder, recurrent layer, and a decoder."""

    def __init__(self, mode, vocab_size, num_embed, num_hidden,
                 num_layers, dropout=0.5, tie_weights=False, **kwargs):
        super(RNNModel, self).__init__(**kwargs)
        with self.name_scope():
            self.drop = nn.Dropout(dropout)
            self.encoder = nn.Embedding(vocab_size, num_embed,
                                        weight_initializer=mx.init.Uniform(0.1))
            if mode == 'rnn_relu':
                self.rnn = rnn.RNN(num_hidden, 'relu', num_layers, dropout=dropout,
                                   input_size=num_embed)
            elif mode == 'rnn_tanh':
                self.rnn = rnn.RNN(num_hidden, num_layers, dropout=dropout,
                                   input_size=num_embed)
            elif mode == 'lstm':
                self.rnn = rnn.LSTM(num_hidden, num_layers, dropout=dropout,
                                    input_size=num_embed)
            elif mode == 'gru':
                self.rnn = rnn.GRU(num_hidden, num_layers, dropout=dropout,
                                   input_size=num_embed)
            else:
                raise ValueError("Invalid mode %s. Options are rnn_relu, "
                                 "rnn_tanh, lstm, and gru"%mode)

            if tie_weights:
                self.decoder = nn.Dense(vocab_size, in_units=num_hidden,
                                        params=self.encoder.params)
            else:
                self.decoder = nn.Dense(vocab_size, in_units=num_hidden)

            self.num_hidden = num_hidden

    def forward(self, inputs, hidden):
        emb = self.drop(self.encoder(inputs))
        output, hidden = self.rnn(emb, hidden)
        output = self.drop(output)
        decoded = self.decoder(output.reshape((-1, self.num_hidden)))
        return decoded, hidden

    def begin_state(self, *args, **kwargs):
        return self.rnn.begin_state(*args, **kwargs)
