use abcmeta

tensorpack/dataflow/base.py

@@ -3,11 +3,14 @@
 # File: base.py
 # Author: Yuxin Wu <ppwwyyxx@gmail.com>
 
-from abc import abstractmethod
+
+from abc import abstractmethod, ABCMeta
 
 __all__ = ['DataFlow']
 
 class DataFlow(object):
+    __metaclass__ = ABCMeta
+
     @abstractmethod
     def get_data(self):
         """

tensorpack/utils/callback.py

@@ -8,13 +8,14 @@ import sys
 import numpy as np
 import os
 import time
-from abc import abstractmethod
+from abc import abstractmethod, ABCMeta
 
 from . import create_test_session
 from .naming import *
 import logger
 
 class Callback(object):
+    __metaclass__ = ABCMeta
     running_graph = 'train'
     """ The graph that this callback should run on.
         Either 'train' or 'test'

tensorpack/utils/sessinit.py

@@ -3,12 +3,14 @@
 # File: sessinit.py
 # Author: Yuxin Wu <ppwwyyxx@gmail.com>
 
-from abc import abstractmethod
+from abc import abstractmethod, ABCMeta
 import numpy as np
 import tensorflow as tf
 
 import logger
 class SessionInit(object):
+    __metaclass__ = ABCMeta
+
     @abstractmethod
     def init(self, sess):
         """ Method to initialize a session"""