Fix sequence bug (#9513)

* Made Sequence iterable

* Made it python2 compliant

keras/engine/training.py

@@ -2162,7 +2162,10 @@ class Model(Container):
                         val_enqueuer.start(workers=workers, max_queue_size=max_queue_size)
                         validation_generator = val_enqueuer.get()
                     else:
-                        validation_generator = validation_data
+                        if isinstance(validation_data, Sequence):
+                            validation_generator = iter(validation_data)
+                        else:
+                            validation_generator = validation_data
                 else:
                     if len(validation_data) == 2:
                         val_x, val_y = validation_data
@@ -2194,7 +2197,10 @@ class Model(Container):
                 enqueuer.start(workers=workers, max_queue_size=max_queue_size)
                 output_generator = enqueuer.get()
             else:
-                output_generator = generator
+                if is_sequence:
+                    output_generator = iter(generator)
+                else:
+                    output_generator = generator
 
             callback_model.stop_training = False
             # Construct epoch logs.
@@ -2366,7 +2372,10 @@ class Model(Container):
                 enqueuer.start(workers=workers, max_queue_size=max_queue_size)
                 output_generator = enqueuer.get()
             else:
-                output_generator = generator
+                if is_sequence:
+                    output_generator = iter(generator)
+                else:
+                    output_generator = generator
 
             while steps_done < steps:
                 generator_output = next(output_generator)
@@ -2490,7 +2499,10 @@ class Model(Container):
                 enqueuer.start(workers=workers, max_queue_size=max_queue_size)
                 output_generator = enqueuer.get()
             else:
-                output_generator = generator
+                if is_sequence:
+                    output_generator = iter(generator)
+                else:
+                    output_generator = generator
 
             if verbose == 1:
                 progbar = Progbar(target=steps)

keras/utils/data_utils.py

@@ -366,6 +366,12 @@ class Sequence(object):
         """
         pass
 
+    def __iter__(self):
+        """Create an infinite generator that iterate over the Sequence."""
+        while True:
+            for item in (self[i] for i in range(len(self))):
+                yield item
+
 
 # Global variables to be shared across processes
 _SHARED_SEQUENCES = {}

tests/test_multiprocessing.py

@@ -6,12 +6,21 @@ import numpy as np
 from keras.models import Sequential
 from keras.layers.core import Dense
 from keras.utils.test_utils import keras_test
+from keras.utils import Sequence
 
 STEPS_PER_EPOCH = 100
 STEPS = 100
 WORKERS = 4
 
 
+class DummySequence(Sequence):
+    def __getitem__(self, idx):
+        return np.zeros([10, 2]), np.ones([10])
+
+    def __len__(self):
+        return 10
+
+
 @pytest.fixture
 def in_tmpdir(tmpdir):
     """Runs a function in a temporary directory.
@@ -175,6 +184,22 @@ def test_multiprocessing_training():
                         workers=0,
                         use_multiprocessing=False)
 
+    # - For Sequence
+    model.fit_generator(DummySequence(),
+                        steps_per_epoch=STEPS_PER_EPOCH,
+                        validation_data=custom_generator(True),
+                        validation_steps=1,
+                        max_queue_size=10,
+                        workers=0,
+                        use_multiprocessing=True)
+    model.fit_generator(DummySequence(),
+                        steps_per_epoch=STEPS_PER_EPOCH,
+                        validation_data=custom_generator(True),
+                        validation_steps=1,
+                        max_queue_size=10,
+                        workers=0,
+                        use_multiprocessing=False)
+
     # Test invalid use cases
     def invalid_generator():
         while True: