From 7be94e033557ec984f53f8a67bd3326ee5a83b4a Mon Sep 17 00:00:00 2001
From: Jon Dufresne <jon.dufresne@gmail.com>
Date: Thu, 27 Apr 2017 05:16:19 -0700
Subject: [PATCH] Replaced set |= operator with update() to avoid temporary
 set.

---
 django/db/models/base.py      | 2 +-
 django/db/models/sql/query.py | 2 +-
 django/test/utils.py          | 7 ++-----
 3 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/django/db/models/base.py b/django/db/models/base.py
index 3c1cb9a1198..28c26990439 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -204,7 +204,7 @@ class ModelBase(type):
             if base not in parents or not hasattr(base, '_meta'):
                 # Things without _meta aren't functional models, so they're
                 # uninteresting parents.
-                inherited_attributes |= set(base.__dict__.keys())
+                inherited_attributes.update(base.__dict__)
                 continue
 
             parent_fields = base._meta.local_fields + base._meta.local_many_to_many
diff --git a/django/db/models/sql/query.py b/django/db/models/sql/query.py
index 5c3eca0032b..a1c1c4be384 100644
--- a/django/db/models/sql/query.py
+++ b/django/db/models/sql/query.py
@@ -1017,7 +1017,7 @@ class Query:
                     )
                     # The used_joins for a tuple of expressions is the union of
                     # the used_joins for the individual expressions.
-                    used_joins |= set(k for k, v in self.alias_refcount.items() if v > pre_joins.get(k, 0))
+                    used_joins.update(k for k, v in self.alias_refcount.items() if v > pre_joins.get(k, 0))
         # For Oracle '' is equivalent to null. The check needs to be done
         # at this stage because join promotion can't be done at compiler
         # stage. Using DEFAULT_DB_ALIAS isn't nice, but it is the best we
diff --git a/django/test/utils.py b/django/test/utils.py
index efd1b49c88f..9ba24a3e77a 100644
--- a/django/test/utils.py
+++ b/django/test/utils.py
@@ -7,6 +7,7 @@ import warnings
 from contextlib import contextmanager
 from functools import wraps
 from io import StringIO
+from itertools import chain
 from types import SimpleNamespace
 from unittest import TestCase, skipIf, skipUnless
 from xml.dom.minidom import Node, parseString
@@ -85,11 +86,7 @@ class ContextList(list):
         """
         Flattened keys of subcontexts.
         """
-        keys = set()
-        for subcontext in self:
-            for dict in subcontext:
-                keys |= set(dict.keys())
-        return keys
+        return set(chain.from_iterable(d for subcontext in self for d in subcontext))
 
 
 def instrumented_test_render(self, context):