[Tune] Better error when using checkpoint_freq (#9998)

python/ray/tune/examples/cifar10_pytorch.py

@@ -195,8 +195,7 @@ def main(num_samples=10, max_num_epochs=10, gpus_per_trial=2):
         config=config,
         num_samples=num_samples,
         scheduler=scheduler,
-        progress_reporter=reporter,
-        checkpoint_at_end=True)
+        progress_reporter=reporter)
 
     best_trial = result.get_best_trial("loss", "min", "last")
     print("Best trial config: {}".format(best_trial.config))

python/ray/tune/experiment.py

@@ -120,13 +120,12 @@ class Experiment:
                  restore=None):
 
         config = config or {}
-
         if callable(run) and detect_checkpoint_function(run):
             if checkpoint_at_end:
-                raise ValueError(
-                    "'checkpoint_at_end' cannot be used with a "
-                    "checkpointable function. You can specify and register "
-                    "checkpoints within your trainable function.")
+                raise ValueError("'checkpoint_at_end' cannot be used with a "
+                                 "checkpointable function. You can specify "
+                                 "and register checkpoints within "
+                                 "your trainable function.")
             if checkpoint_freq:
                 raise ValueError(
                     "'checkpoint_freq' cannot be used with a "

python/ray/tune/tests/test_function_api.py

@@ -300,6 +300,15 @@ class FunctionApiTest(unittest.TestCase):
         ray.shutdown()
         _register_all()  # re-register the evicted objects
 
+    def testCheckpointError(self):
+        def train(config, checkpoint_dir=False):
+            pass
+
+        with self.assertRaises(ValueError):
+            tune.run(train, checkpoint_freq=1)
+        with self.assertRaises(ValueError):
+            tune.run(train, checkpoint_at_end=True)
+
     def testCheckpointFunctionAtEnd(self):
         def train(config, checkpoint_dir=False):
             for i in range(10):

python/ray/tune/tune.py

@@ -264,10 +264,9 @@ def run(run_or_experiment,
 
     for i, exp in enumerate(experiments):
         if not isinstance(exp, Experiment):
-            run_identifier = Experiment.register_if_needed(exp)
             experiments[i] = Experiment(
                 name=name,
-                run=run_identifier,
+                run=exp,
                 stop=stop,
                 config=config,
                 resources_per_trial=resources_per_trial,