[tune] use dated experiment dir per default (#11104)

python/ray/tune/utils/util.py

@@ -5,6 +5,7 @@ import inspect
 import threading
 import time
 from collections import defaultdict, deque, Mapping, Sequence
+from datetime import datetime
 from threading import Thread
 
 import numpy as np
@@ -153,6 +154,10 @@ class Tee(object):
         self.stream2.flush(*args, **kwargs)
 
 
+def date_str():
+    return datetime.today().strftime("%Y-%m-%d_%H-%M-%S")
+
+
 def env_integer(key, default):
     # TODO(rliaw): move into ray.constants
     if key in os.environ: