[tune] hyperband (#1156)

* trial scheduler interface

* remove

* wip median stopping

* remove

* median stopping rule

* update

* docs

* update

* Revrt

* update

* hyperband untested

* small changes before moving on

* added endpoints

* good changes

* init tests

* smore tests

* unfinished tests

* testing

* testing code

* morbugs

* fixes

* end

* tests and typo

* nit

* try this

* tests

* testing

* lint

* lint

* lint

* comments and docs

* almost screwed up

* lint

python/ray/tune/trial_scheduler.py

@@ -12,6 +12,18 @@ class TrialScheduler(object):
     PAUSE = "PAUSE"
     STOP = "STOP"
 
+    def on_trial_add(self, trial_runner, trial):
+        """Called when a new trial is added to the trial runner."""
+
+        raise NotImplementedError
+
+    def on_trial_error(self, trial_runner, trial):
+        """Notification for the error of trial.
+
+        This will only be called when the trial is in the RUNNING state."""
+
+        raise NotImplementedError
+
     def on_trial_result(self, trial_runner, trial, result):
         """Called on each intermediate result returned by a trial.
 
@@ -44,6 +56,12 @@ class TrialScheduler(object):
 class FIFOScheduler(TrialScheduler):
     """Simple scheduler that just runs trials in submission order."""
 
+    def on_trial_add(self, trial_runner, trial):
+        pass
+
+    def on_trial_error(self, trial_runner, trial):
+        pass
+
     def on_trial_result(self, trial_runner, trial, result):
         return TrialScheduler.CONTINUE