[tune] Tune onto Logging Module (#2882)

Moves Tune onto logging in Python. Ignores examples and tests.

python/ray/tune/trial_executor.py

@@ -3,10 +3,13 @@ from __future__ import absolute_import
 from __future__ import division
 from __future__ import print_function
 
+import logging
 import traceback
 
 from ray.tune.trial import Trial, Checkpoint
 
+logger = logging.getLogger(__name__)
+
 
 class TrialExecutor(object):
     """Manages platform-specific details such as resource handling
@@ -66,14 +69,15 @@ class TrialExecutor(object):
             error_msg (str): Optional error message.
         """
         try:
-            print("Attempting to recover trial state from last checkpoint")
+            logger.info(
+                "Attempting to recover trial state from last checkpoint")
             self.stop_trial(
                 trial, error=True, error_msg=error_msg, stop_logger=False)
             trial.result_logger.flush()
             self.start_trial(trial)
         except Exception:
             error_msg = traceback.format_exc()
-            print("Error recovering trial from checkpoint, abort:", error_msg)
+            logger.exception("Error recovering trial from checkpoint, abort.")
             self.stop_trial(trial, error=True, error_msg=error_msg)
 
     def continue_training(self, trial):
@@ -92,7 +96,7 @@ class TrialExecutor(object):
             self.stop_trial(trial, stop_logger=False)
             trial.status = Trial.PAUSED
         except Exception:
-            print("Error pausing runner:", traceback.format_exc())
+            logger.exception("Error pausing runner.")
             trial.status = Trial.ERROR
 
     def unpause_trial(self, trial):