From 964c3d55f00f2da10c2a69f3817408a40f9136ec Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Sat, 21 Sep 2024 21:44:42 +0200
Subject: [PATCH] Speed up finding the reason if its unset (#9175)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
(cherry picked from commit 756fae80b824bf1606235962bd2b460b63da4da0)
---
 CHANGES/9175.misc.rst      |  1 +
 aiohttp/web_response.py    | 16 +++++++++-------
 tests/test_web_response.py |  8 ++++++++
 3 files changed, 18 insertions(+), 7 deletions(-)
 create mode 120000 CHANGES/9175.misc.rst

diff --git a/CHANGES/9175.misc.rst b/CHANGES/9175.misc.rst
new file mode 120000
index 00000000000..d6a2f2aaaab
--- /dev/null
+++ b/CHANGES/9175.misc.rst
@@ -0,0 +1 @@
+9174.misc.rst
\ No newline at end of file
diff --git a/aiohttp/web_response.py b/aiohttp/web_response.py
index bf184980700..57b3941bcc0 100644
--- a/aiohttp/web_response.py
+++ b/aiohttp/web_response.py
@@ -42,6 +42,8 @@
 from .payload import Payload
 from .typedefs import JSONEncoder, LooseHeaders
 
+REASON_PHRASES = {http_status.value: http_status.phrase for http_status in HTTPStatus}
+
 __all__ = ("ContentCoding", "StreamResponse", "Response", "json_response")
 
 
@@ -102,7 +104,7 @@ def __init__(
         else:
             self._headers = CIMultiDict()
 
-        self.set_status(status, reason)
+        self._set_status(status, reason)
 
     @property
     def prepared(self) -> bool:
@@ -139,13 +141,13 @@ def set_status(
         assert (
             not self.prepared
         ), "Cannot change the response status code after the headers have been sent"
-        self._status = int(status)
+        self._set_status(status, reason)
+
+    def _set_status(self, status: int, reason: Optional[str]) -> None:
+        self._status = status
         if reason is None:
-            try:
-                reason = HTTPStatus(self._status).phrase
-            except ValueError:
-                reason = ""
-        if "\n" in reason:
+            reason = REASON_PHRASES.get(self._status, "")
+        elif "\n" in reason:
             raise ValueError("Reason cannot contain \\n")
         self._reason = reason
 
diff --git a/tests/test_web_response.py b/tests/test_web_response.py
index ec9522b05a5..080edaf57c3 100644
--- a/tests/test_web_response.py
+++ b/tests/test_web_response.py
@@ -933,6 +933,14 @@ def test_set_status_with_reason() -> None:
     assert "Everything is fine!" == resp.reason
 
 
+def test_set_status_with_empty_reason() -> None:
+    resp = StreamResponse()
+
+    resp.set_status(200, "")
+    assert resp.status == 200
+    assert resp.reason == ""
+
+
 async def test_start_force_close() -> None:
     req = make_request("GET", "/")
     resp = StreamResponse()