Use of six.PY3 should be forward compatible

Care should be taken in using a condition like so:
if six.PY3:
  foo()
else:
  bar()

This assumes PY2 and PY4 would behave the same.  Rather the
conditional should check for PY2 and use the else for PY3 and
future versions of Python.

http://astrofrog.github.io/blog/2016/01/12/stop-writing-python-4-incompatible-code/

Change-Id: I9bc00e2f01fe8fe970d6c5327207c08a90885cda

nova/api/openstack/urlmap.py

@@ -19,10 +19,10 @@ from oslo_log import log as logging
 import paste.urlmap
 import six
 
-if six.PY3:
-    from urllib import request as urllib2
-else:
+if six.PY2:
     import urllib2
+else:
+    from urllib import request as urllib2
 
 from nova.api.openstack import wsgi
 

nova/cells/utils.py

@@ -105,10 +105,10 @@ class _CellProxy(object):
                 else:
                     yield name, getattr(self._obj, name)
 
-    if six.PY3:
-        items = _iteritems
-    else:
+    if six.PY2:
         iteritems = _iteritems
+    else:
+        items = _iteritems
 
     def __getattr__(self, key):
         return getattr(self._obj, key)

nova/openstack/common/cliutils.py

@@ -180,10 +180,10 @@ def print_list(objs, fields, formatters=None, sortby_index=0,
                 row.append(data)
         pt.add_row(row)
 
-    if six.PY3:
-        print(encodeutils.safe_encode(pt.get_string(**kwargs)).decode())
-    else:
+    if six.PY2:
         print(encodeutils.safe_encode(pt.get_string(**kwargs)))
+    else:
+        print(encodeutils.safe_encode(pt.get_string(**kwargs)).decode())
 
 
 def print_dict(dct, dict_property="Property", wrap=0, dict_value='Value'):
@@ -213,10 +213,10 @@ def print_dict(dct, dict_property="Property", wrap=0, dict_value='Value'):
         else:
             pt.add_row([k, v])
 
-    if six.PY3:
-        print(encodeutils.safe_encode(pt.get_string()).decode())
-    else:
+    if six.PY2:
         print(encodeutils.safe_encode(pt.get_string()))
+    else:
+        print(encodeutils.safe_encode(pt.get_string()).decode())
 
 
 def get_password(max_password_prompts=3):

nova/test.py

@@ -63,13 +63,13 @@ logging.setup(CONF, 'nova')
 
 _TRUE_VALUES = ('True', 'true', '1', 'yes')
 
-if six.PY3:
+if six.PY2:
+    nested = contextlib.nested
+else:
     @contextlib.contextmanager
     def nested(*contexts):
         with contextlib.ExitStack() as stack:
             yield [stack.enter_context(c) for c in contexts]
-else:
-    nested = contextlib.nested
 
 
 class SampleNetworks(fixtures.Fixture):

nova/tests/unit/test_exception.py

@@ -124,12 +124,12 @@ class NovaExceptionTestCase(test.NoDBTestCase):
         class FakeNovaException_Remote(exception.NovaException):
             msg_fmt = "some message"
 
-            if six.PY3:
-                def __str__(self):
-                    return "print the whole trace"
-            else:
+            if six.PY2:
                 def __unicode__(self):
                     return u"print the whole trace"
+            else:
+                def __str__(self):
+                    return "print the whole trace"
 
         exc = FakeNovaException_Remote()
         self.assertEqual(u"print the whole trace", six.text_type(exc))

nova/utils.py

@@ -722,12 +722,12 @@ def monkey_patch():
     # If CONF.monkey_patch is not True, this function do nothing.
     if not CONF.monkey_patch:
         return
-    if six.PY3:
+    if six.PY2:
+        is_method = inspect.ismethod
+    else:
         def is_method(obj):
             # Unbound methods became regular functions on Python 3
             return inspect.ismethod(obj) or inspect.isfunction(obj)
-    else:
-        is_method = inspect.ismethod
     # Get list of modules and decorators
     for module_and_decorator in CONF.monkey_patch_modules:
         module, decorator_name = module_and_decorator.split(':')

nova/virt/libvirt/host.py

@@ -63,7 +63,7 @@ LOG = logging.getLogger(__name__)
 
 native_socket = patcher.original('socket')
 native_threading = patcher.original("threading")
-native_Queue = patcher.original("queue" if six.PY3 else "Queue")
+native_Queue = patcher.original("Queue" if six.PY2 else "queue")
 
 CONF = cfg.CONF
 CONF.import_opt('host', 'nova.netconf')