Make it possible for a subclassed model to be compiled and trained with no

external loss.

PiperOrigin-RevId: 248035588

tensorflow/python/keras/engine/training.py

@@ -592,6 +592,7 @@ class Model(network.Network):
       epochs = kwargs.pop('nb_epoch')
     if kwargs:
       raise TypeError('Unrecognized keyword arguments: ' + str(kwargs))
+    self._assert_compile_was_called()
 
     # Case 1: distribution strategy.
     if self._distribution_strategy:
@@ -862,6 +863,8 @@ class Model(network.Network):
         ValueError: in case of invalid arguments.
     """
     _keras_api_gauge.get_cell('evaluate').set(True)
+    self._assert_compile_was_called()
+
     # Case 1: distribution strategy.
     if self._distribution_strategy:
       if K.in_multi_worker_mode():
@@ -1133,6 +1136,7 @@ class Model(network.Network):
     Raises:
       ValueError: In case of invalid user-provided arguments.
     """
+    self._assert_compile_was_called()
     # If at this point we are in the replica context, then it is okay to execute
     # the Eager code path.  The expected way to get here is to call `fit` that
     # calls `train_on_batch` on each replica.
@@ -1213,6 +1217,7 @@ class Model(network.Network):
     Raises:
         ValueError: In case of invalid user-provided arguments.
     """
+    self._assert_compile_was_called()
     if (self._distribution_strategy and
         distribution_strategy_context.in_cross_replica_context()):
       raise NotImplementedError('`test_on_batch` is not supported for models '
@@ -2191,8 +2196,6 @@ class Model(network.Network):
     metrics_tensors = [
         self._all_metrics_tensors[m] for m in self.metrics_names[1:]
     ]
-    if not self._is_compiled:
-      raise RuntimeError('You must compile your model before using it.')
     self._check_trainable_weights_consistency()
     # If we have re-compiled the loss/weighted metric sub-graphs then create
     # train function even if one exists already. This is because
@@ -2229,8 +2232,6 @@ class Model(network.Network):
     metrics_tensors = [
         self._all_metrics_tensors[m] for m in self.metrics_names[1:]
     ]
-    if not self._is_compiled:
-      raise RuntimeError('You must compile your model before using it.')
     # If we have re-compiled the loss/weighted metric sub-graphs then create
     # test function even if one exists already. This is because
     # `_feed_sample_weights` list has been updated on re-copmpile.
@@ -2555,13 +2556,9 @@ class Model(network.Network):
       y_input = y
       dict_inputs = isinstance(self.inputs, dict)
 
-    if y_input is not None:
-      if not self.optimizer:
-        raise RuntimeError('You must compile a model before '
-                           'training/testing. '
-                           'Use `model.compile(optimizer, loss)`.')
-      if not self._is_compiled:
+    if not self._is_compiled and self.optimizer:
       # On-the-fly compilation of the model.
+      if y_input is not None:
         # We need to use `y` to set the model targets.
         if training_utils.has_tensors(y_input):
           y_input = training_utils.cast_if_floating_dtype(y_input)
@@ -2594,9 +2591,12 @@ class Model(network.Network):
         target_tensors = None
       else:
         # Handle target tensors if any passed.
+        if y_input is not None:
           if not isinstance(y_input, (list, tuple)):
             y_input = [y_input]
           target_tensors = [v for v in y_input if _is_symbolic_tensor(v)]
+        else:
+          target_tensors = None
       is_compile_called = True
       self.compile(
           optimizer=self.optimizer,
@@ -2921,6 +2921,16 @@ class Model(network.Network):
       return int(self._ckpt_saved_epoch) + 1
     return initial_epoch
 
+  def _assert_compile_was_called(self):
+    # Checks whether `compile` has been called. If it has been called,
+    # then the optimizer is set. This is different from whether the
+    # model is compiled
+    # (i.e. whether the model is built and its inputs/outputs are set).
+    if not self.optimizer:
+      raise RuntimeError('You must compile your model before '
+                         'training/testing. '
+                         'Use `model.compile(optimizer, loss)`.')
+
 
 class DistributedCallbackModel(Model):
   """Model that is used for callbacks with tf.distribute.Strategy."""

tensorflow/python/keras/engine/training_eager.py

@@ -339,10 +339,12 @@ def test_on_batch(model,
     if len(inputs) and tensor_util.is_tensor(inputs[0]):
       inputs = training_utils.cast_if_floating_to_model_input_dtypes(inputs,
                                                                      model)
+      if targets:
         targets = training_utils.cast_if_floating_dtype(targets)
     else:
       inputs = training_utils.cast_if_floating_to_model_input_dtypes(
           [ops.convert_to_tensor(val) for val in inputs], model)
+      if targets:
         targets = training_utils.cast_if_floating_dtype(
             [ops.convert_to_tensor(val) for val in targets])
   if sample_weights:

tensorflow/python/keras/engine/training_test.py

@@ -1201,8 +1201,7 @@ class TrainingTest(keras_parameterized.TestCase):
     inputs = keras.Input(shape=(1,))
     outputs = keras.layers.Dense(1)(inputs)
     model = keras.Model(inputs, outputs)
-    with self.assertRaisesRegex(
-        RuntimeError, 'You must compile a model before training/testing.'):
+    with self.assertRaisesRegex(RuntimeError, 'must compile your model'):
       model.fit(np.ones((1, 1)), np.ones((1, 1)))
 
     class MyModel(keras.Model):
@@ -1212,10 +1211,7 @@ class TrainingTest(keras_parameterized.TestCase):
         return x
 
     model = MyModel()
-    model.compile(keras.optimizers.Adam(1e-3))
-
-    with self.assertRaisesRegex(RuntimeError,
-                                'You must compile your model before using it.'):
+    with self.assertRaisesRegex(RuntimeError, 'must compile your model'):
       model.fit(np.random.random((32, 1)), epochs=2)
 
 

tensorflow/python/keras/model_subclassing_test.py

@@ -31,6 +31,7 @@ from tensorflow.python.framework import test_util
 from tensorflow.python.keras import keras_parameterized
 from tensorflow.python.keras import testing_utils
 from tensorflow.python.ops import array_ops
+from tensorflow.python.ops import math_ops
 from tensorflow.python.ops import embedding_ops
 from tensorflow.python.ops import init_ops
 from tensorflow.python.ops import resource_variable_ops
@@ -992,6 +993,28 @@ class ModelSubclassCompiledTest(keras_parameterized.TestCase):
     loss = model.train_on_batch(x, y)
     self.assertGreater(loss, 0.1)
 
+  def test_no_loss_in_compile(self):
+
+    class InternalLossModel(keras.Model):
+
+      def __init__(self):
+        super(InternalLossModel, self).__init__()
+        self.dense = keras.layers.Dense(1)
+
+      def call(self, inputs):
+        out = self.dense(inputs)
+        self.add_loss(math_ops.reduce_sum(out))
+        return out
+
+    model = InternalLossModel()
+    x = np.ones((10, 10))
+    model.predict(x)
+    model.compile(
+        optimizer='rmsprop',
+        run_eagerly=testing_utils.should_run_eagerly())
+    model.fit(x)
+    model.evaluate(x)
+
 
 class GraphSpecificModelSubclassingTests(test.TestCase):