diff -r e3c9a47a83fb Lib/concurrent/futures/_base.py
--- a/Lib/concurrent/futures/_base.py	Mon Apr 11 17:33:27 2016 +0300
+++ b/Lib/concurrent/futures/_base.py	Thu Apr 21 19:57:42 2016 +0800
@@ -3,6 +3,7 @@
 
 __author__ = 'Brian Quinlan (brian@sweetapp.com)'
 
+import abc
 import collections
 import logging
 import threading
@@ -53,7 +54,7 @@
     """The operation exceeded the given deadline."""
     pass
 
-class _Waiter(object):
+class _Waiter:
     """Provides the event that wait() and as_completed() block on."""
     def __init__(self):
         self.event = threading.Event()
@@ -135,7 +136,7 @@
         super().add_cancelled(future)
         self._decrement_pending_calls()
 
-class _AcquireFutures(object):
+class _AcquireFutures:
     """A context manager that does an ordered acquire of Future conditions."""
 
     def __init__(self, futures):
@@ -279,7 +280,7 @@
     done.update(waiter.finished_futures)
     return DoneAndNotDoneFutures(done, set(fs) - done)
 
-class Future(object):
+class Future:
     """Represents the result of an asynchronous computation."""
 
     def __init__(self):
@@ -506,9 +507,10 @@
             self._condition.notify_all()
         self._invoke_callbacks()
 
-class Executor(object):
+class Executor(metaclass=abc.ABCMeta):
     """This is an abstract base class for concrete asynchronous executors."""
 
+    @abc.abstractmethod
     def submit(self, fn, *args, **kwargs):
         """Submits a callable to be executed with the given arguments.
 
@@ -518,7 +520,7 @@
         Returns:
             A Future representing the given call.
         """
-        raise NotImplementedError()
+        raise NotImplementedError
 
     def map(self, fn, *iterables, timeout=None, chunksize=1):
         """Returns an iterator equivalent to map(fn, iter).
diff -r e3c9a47a83fb Lib/concurrent/futures/process.py
--- a/Lib/concurrent/futures/process.py	Mon Apr 11 17:33:27 2016 +0300
+++ b/Lib/concurrent/futures/process.py	Thu Apr 21 19:57:42 2016 +0800
@@ -112,20 +112,20 @@
     exc.__cause__ = _RemoteTraceback(tb)
     return exc
 
-class _WorkItem(object):
+class _WorkItem:
     def __init__(self, future, fn, args, kwargs):
         self.future = future
         self.fn = fn
         self.args = args
         self.kwargs = kwargs
 
-class _ResultItem(object):
+class _ResultItem:
     def __init__(self, work_id, exception=None, result=None):
         self.work_id = work_id
         self.exception = exception
         self.result = result
 
-class _CallItem(object):
+class _CallItem:
     def __init__(self, work_id, fn, args, kwargs):
         self.work_id = work_id
         self.fn = fn
diff -r e3c9a47a83fb Lib/concurrent/futures/thread.py
--- a/Lib/concurrent/futures/thread.py	Mon Apr 11 17:33:27 2016 +0300
+++ b/Lib/concurrent/futures/thread.py	Thu Apr 21 19:57:42 2016 +0800
@@ -40,7 +40,7 @@
 
 atexit.register(_python_exit)
 
-class _WorkItem(object):
+class _WorkItem:
     def __init__(self, future, fn, args, kwargs):
         self.future = future
         self.fn = fn