[tune] Remove rllib dep again, and add a test (#1792)

* tune should not depend on rllib

* fix dep test

* Tue Mar 27 16:55:41 PDT 2018

* f401

python/ray/tune/test/dependency_test.py

@@ -0,0 +1,26 @@
+#!/usr/bin/env python
+
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import sys
+
+import ray
+from ray.tune import register_trainable, run_experiments
+
+
+def f(config, reporter):
+    reporter(timesteps_total=1)
+
+
+if __name__ == "__main__":
+    ray.init()
+    register_trainable("my_class", f)
+    run_experiments({
+        "test": {
+            "run": "my_class",
+            "stop": {"training_iteration": 1}
+        }
+    })
+    assert 'ray.rllib' not in sys.modules, "RLlib should not be imported"

python/ray/tune/trial.py

@@ -56,6 +56,11 @@ class Resources(
         return self.gpu + self.extra_gpu
 
 
+def has_trainable(trainable_name):
+    return ray.tune.registry._default_registry.contains(
+        ray.tune.registry.TRAINABLE_CLASS, trainable_name)
+
+
 class Trial(object):
     """A trial object holds the state for one model training run.
 
@@ -83,9 +88,11 @@ class Trial(object):
         in ray.tune.config_parser.
         """
 
-        if not ray.tune.registry._default_registry.contains(
-                ray.tune.registry.TRAINABLE_CLASS, trainable_name):
-            raise TuneError("Unknown trainable: " + trainable_name)
+        if not has_trainable(trainable_name):
+            # Make sure rllib agents are registered
+            from ray import rllib  # noqa: F401
+            if not has_trainable(trainable_name):
+                raise TuneError("Unknown trainable: " + trainable_name)
 
         if stopping_criterion:
             for k in stopping_criterion:

python/ray/tune/tune.py

@@ -49,9 +49,6 @@ def run_experiments(experiments, scheduler=None, with_server=False,
         verbose (bool): How much output should be printed for each trial.
     """
 
-    # Make sure rllib agents are registered
-    from ray import rllib  # noqa # pylint: disable=unused-import
-
     if scheduler is None:
         scheduler = FIFOScheduler()