refactor: RequestGroup.is_empty() and .strip_zeros()

This makes an is_empty() method on RequestGroup which answers whether
the group has any resources, traits, or aggregates; and a strip_zeros()
method which removes any resources whose amount is zero.

These are used to refactor ResourceRequest.strip_zeros().
_clean_empties() becomes not worth keeping in its own method, so it's
rolled into ResourceRequest.strip_zeros(), its only consumer. At the
same time, the worthless (at least now that we're py3-only)
ResourceRequest.resource_groups() generator is removed and inlined in
the couple of places it was used.

In addition to simply making the code more cohesive, a later patch will
make use of RequestGroup.is_empty() to forbid no-op groups coming from
ports, accelerators, etc.

Change-Id: I6a83b0eb0f1c352f197f2ef8fab124decd537270

nova/objects/request_spec.py

@@ -1153,3 +1153,15 @@ class RequestGroup(base.NovaObject):
             LOG.warning(
                 "Only (%(tvals)s) traits are supported. Received '%(val)s'.",
                 {"tvals": ', '.join(trait_vals), "val": trait_type})
+
+    def is_empty(self):
+        return not any((
+            self.resources,
+            self.required_traits, self.forbidden_traits,
+            self.aggregates, self.forbidden_aggregates))
+
+    def strip_zeros(self):
+        """Remove any resources whose amount is zero."""
+        for rclass in list(self.resources):
+            if self.resources[rclass] == 0:
+                self.resources.pop(rclass)

nova/scheduler/utils.py

@@ -338,10 +338,6 @@ class ResourceRequest(object):
             return
         self._group_policy = policy
 
-    def resource_groups(self):
-        for rg in self._rg_by_id.values():
-            yield rg.resources
-
     def get_num_of_suffixed_groups(self):
         return len([ident for ident in self._rg_by_id.keys()
                     if ident is not None])
@@ -355,25 +351,19 @@ class ResourceRequest(object):
         :return: A dict of the form {resource_class: amount}
         """
         ret = collections.defaultdict(lambda: 0)
-        for resource_dict in self.resource_groups():
-            for resource_class, amount in resource_dict.items():
+        for rg in self._rg_by_id.values():
+            for resource_class, amount in rg.resources.items():
                 ret[resource_class] += amount
         return dict(ret)
 
-    def _clean_empties(self):
-        """Get rid of any empty RequestGroup instances."""
-        for ident, rg in list(self._rg_by_id.items()):
-            if not any((rg.resources, rg.required_traits,
-                        rg.forbidden_traits)):
-                self._rg_by_id.pop(ident)
-
     def strip_zeros(self):
         """Remove any resources whose amounts are zero."""
-        for resource_dict in self.resource_groups():
-            for rclass in list(resource_dict):
-                if resource_dict[rclass] == 0:
-                    resource_dict.pop(rclass)
-        self._clean_empties()
+        for rg in self._rg_by_id.values():
+            rg.strip_zeros()
+        # Get rid of any empty RequestGroup instances.
+        for ident, rg in list(self._rg_by_id.items()):
+            if rg.is_empty():
+                self._rg_by_id.pop(ident)
 
     def to_querystring(self):
         """Produce a querystring of the form expected by

nova/tests/unit/scheduler/test_utils.py

@@ -698,14 +698,14 @@ class TestUtils(TestUtilsBase):
                 self.context, reqspec, self.mock_host_manager)
         self.assertEqual({'MEMORY_MB': 1024, 'DISK_GB': 15, 'VCPU': 1},
                          req.get_request_group(None).resources)
-        self.assertEqual(1, len(list(req.resource_groups())))
+        self.assertEqual(1, len(list(req._rg_by_id)))
 
         reqspec = objects.RequestSpec(flavor=flavor, requested_resources=[])
         req = utils.resources_from_request_spec(
                 self.context, reqspec, self.mock_host_manager)
         self.assertEqual({'MEMORY_MB': 1024, 'DISK_GB': 15, 'VCPU': 1},
                          req.get_request_group(None).resources)
-        self.assertEqual(1, len(list(req.resource_groups())))
+        self.assertEqual(1, len(list(req._rg_by_id)))
 
     @ddt.data(
         # Test single hint that we are checking for.