Added python2 support and check for outdated tf (#562)

Improve the Evolutionary Strategies example.

examples/evolution_strategies/policies.py

@@ -76,7 +76,7 @@ class Policy:
 
   # === Rollouts/training ===
 
-  def rollout(self, env, *, render=False, timestep_limit=None, save_obs=False,
+  def rollout(self, env, render=False, timestep_limit=None, save_obs=False,
               random_stream=None):
     """Do a rollout.
 

examples/evolution_strategies/tabular_logger.py

@@ -79,12 +79,13 @@ def dump_tabular():
   _Logger.CURRENT.dump_tabular()
 
 
-def log(*args, level=INFO):
+def log(*args, **kwargs):
   """Write the sequence of args, with no separators.
 
   This is written to the console and output files (if you've configured an
   output file).
   """
+  level = kwargs['level'] if 'level' in kwargs else INFO
   _Logger.CURRENT.log(*args, level=level)
 
 
@@ -177,7 +178,8 @@ class _Logger(object):
       self.tbwriter.write_values(self.name2val)
       self.name2val.clear()
 
-  def log(self, *args, level=INFO):
+  def log(self, *args, **kwargs):
+    level = kwargs['level'] if 'level' in kwargs else INFO
     if self.level <= level:
       self._do_log(*args)
 
@@ -198,7 +200,7 @@ class _Logger(object):
   # Misc
 
   def _do_log(self, *args):
-    self._write_text(*args, '\n')
+    self._write_text(*args + ('\n',))
     for f in self.text_outputs:
       try:
         f.flush()

examples/evolution_strategies/tf_util.py

@@ -10,6 +10,11 @@ import tensorflow as tf
 import functools
 import os
 
+# Tensorflow must be at least version 1.0.0 for the example to work.
+if int(tf.__version__.split(".")[0]) < 1:
+  raise Exception("Your Tensorflow version is less than 1.0.0. Please update "
+                  "Tensorflow to the latest version.")
+
 # ================================================================
 # Import all names into common namespace
 # ================================================================