'Creates logits for a character if required.
Args:
inputs: A tensor with shape [batch_size, ?] (depth is implementation
dependent).
char_index: A integer index of a character in the output sequence.
Returns:
A tensor with shape [batch_size, num_char_classes]'

def char_logit(self, inputs, char_index):

    if (char_index not in self._char_logits):
        self._char_logits[char_index] = tf.nn.xw_plus_b(inputs, self._softmax_w, self._softmax_b)
    return self._char_logits[char_index]
