Import modules, not classes

This addresses comments from I24b13c8654a33d99bf687a44a36cfdace39e3866
to follow guidelines to only import modules, not classes.

Change-Id: I0e66c08bfcdff306bac0121602d45b56cfb2c712
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>

2 files changed, 4 insertions, 9 deletions

diff --git a/taskflow/conductors/backends/impl_executor.py b/taskflow/conductors/backends/impl_executor.py
index 99c3e5e..ab55821 100644
--- a/taskflow/conductors/backends/impl_executor.py
+++ b/taskflow/conductors/backends/impl_executor.py
@@ -13,15 +13,11 @@
 #    under the License.
 
 import abc
+import contextlib
 import functools
 import itertools
 import threading
 
-try:
-    from contextlib import ExitStack  # noqa
-except ImportError:
-    from contextlib2 import ExitStack  # noqa
-
 from oslo_utils import excutils
 from oslo_utils import timeutils
 import six
@@ -154,7 +150,7 @@ class ExecutorConductor(base.Conductor):
     def _dispatch_job(self, job):
         engine = self._engine_from_job(job)
         listeners = self._listeners_from_job(job, engine)
-        with ExitStack() as stack:
+        with contextlib.ExitStack() as stack:
             for listener in listeners:
                 stack.enter_context(listener)
             self._log.debug("Dispatching engine for job '%s'", job)
diff --git a/taskflow/types/sets.py b/taskflow/types/sets.py
index bbd988d..1a33ed3 100644
--- a/taskflow/types/sets.py
+++ b/taskflow/types/sets.py
@@ -15,8 +15,7 @@
 #    under the License.
 
 import collections
-from collections.abc import Hashable
-from collections.abc import Set
+from collections import abc
 import itertools
 
 import six
@@ -34,7 +33,7 @@ def _merge_in(target, iterable=None, sentinel=_sentinel):
     return target
 
 
-class OrderedSet(Set, Hashable):
+class OrderedSet(abc.Set, abc.Hashable):
     """A read-only hashable set that retains insertion/initial ordering.
 
     It should work in all existing places that ``frozenset`` is used.