Don't reuse the same cell when creating MultiRNNCell in ptb_word_lm.py

tutorials/rnn/ptb/ptb_word_lm.py

@@ -213,13 +213,15 @@ class PTBModel(object):
     # Slightly better results can be obtained with forget gate biases
     # initialized to 1 but the hyperparameters of the model would need to be
     # different than reported in the paper.
-    cell = self._get_lstm_cell(config, is_training)
-    if is_training and config.keep_prob < 1:
-      cell = tf.contrib.rnn.DropoutWrapper(
-          cell, output_keep_prob=config.keep_prob)
+    def make_cell():
+      cell = self._get_lstm_cell(config, is_training)
+      if is_training and config.keep_prob < 1:
+        cell = tf.contrib.rnn.DropoutWrapper(
+            cell, output_keep_prob=config.keep_prob)
+      return cell
 
     cell = tf.contrib.rnn.MultiRNNCell(
-        [cell for _ in range(config.num_layers)], state_is_tuple=True)
+        [make_cell() for _ in range(config.num_layers)], state_is_tuple=True)
 
     self._initial_state = cell.zero_state(config.batch_size, data_type())
     state = self._initial_state