towards python 2.x support for deep_mimic (still issue with Logger.print2)

examples/pybullet/gym/pybullet_envs/deep_mimic/env/env.py

@@ -1,4 +1,10 @@
-from abc import ABC, abstractmethod
+from abc import  abstractmethod
+import sys, abc
+if sys.version_info >= (3, 4):
+    ABC = abc.ABC
+else:
+    ABC = abc.ABCMeta('ABC', (), {})
+
 import numpy as np
 from enum import Enum
 

examples/pybullet/gym/pybullet_envs/deep_mimic/learning/rl_agent.py

@@ -2,8 +2,14 @@ import numpy as np
 import copy
 import os
 import time
+import sys
+from abc import abstractmethod
+import abc
+if sys.version_info >= (3, 4):
+    ABC = abc.ABC
+else:
+    ABC = abc.ABCMeta('ABC', (), {})
 
-from abc import ABC, abstractmethod
 from enum import Enum
 
 from pybullet_envs.deep_mimic.learning.path import *

examples/pybullet/gym/pybullet_envs/deep_mimic/learning/solvers/solver.py

@@ -1,4 +1,9 @@
-from abc import ABC, abstractmethod
+from abc import abstractmethod
+import sys, abc
+if sys.version_info >= (3, 4):
+    ABC = abc.ABC
+else:
+    ABC = abc.ABCMeta('ABC', (), {})
 
 class Solver(ABC):
     def __init__(self, vars):