Used more augmented assignment statements.

Identified using the following command:

$ git grep -I '\(\<[_a-zA-Z0-9]\+\>\) *= *\1 *[-+/*^%&|<>@]'

1 files changed, 1 insertions, 1 deletions

diff --git a/django/http/response.py b/django/http/response.py
index 7c0db55a5d..bb94e81263 100644
--- a/django/http/response.py
+++ b/django/http/response.py
@@ -241,7 +241,7 @@ class HttpResponseBase:
                 # Add one second so the date matches exactly (a fraction of
                 # time gets lost between converting to a timedelta and
                 # then the date string).
-                delta = delta + datetime.timedelta(seconds=1)
+                delta += datetime.timedelta(seconds=1)
                 # Just set max_age - the max_age logic will set expires.
                 expires = None
                 if max_age is not None: