def compile(self, optimizer, loss, metrics=None):
        """
        Args:
            optimizer (tf.train.Optimizer):
            loss, metrics: string or list of strings
        """
        if isinstance(loss, six.string_types):
            loss = [loss]
        if metrics is None:
            metrics = []
        if isinstance(metrics, six.string_types):
            metrics = [metrics]

        self._stats_to_inference = loss + metrics + [TOTAL_LOSS_NAME]
        setup_keras_trainer(
            self.trainer, get_model=self.get_model,
            input_signature=self.input_signature,
            target_signature=self.target_signature,
            input=self.input,
            optimizer=optimizer,
            loss=loss,
            metrics=metrics)

        Args:
            optimizer (tf.train.Optimizer):
            loss, metrics: string or list of strings
        
tensorpack/contrib/keras.py