From 578f33e282479aa5bb77ee3a4f49122cef2b0a59 Mon Sep 17 00:00:00 2001
From: RedGuy12 <61329810+RedGuy12@users.noreply.github.com>
Date: Wed, 13 Dec 2023 11:20:49 -0600
Subject: [PATCH] fix: In subscripts, treat walruses just like other binary
 operators

Signed-off-by: RedGuy12 <61329810+RedGuy12@users.noreply.github.com>
---
 CHANGES.md                          | 3 +++
 src/black/lines.py                  | 6 +++++-
 tests/data/cases/preview_pep_572.py | 4 ++--
 3 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/CHANGES.md b/CHANGES.md
index 9d79b0fb61a..eeb6bb1fd0b 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -14,6 +14,9 @@
 
 <!-- Changes that affect Black's preview style -->
 
+- Fix bug where spaces were not added around parenthesized walruses in subscripts,
+  unlike other binary operators (#4109)
+
 ### Configuration
 
 <!-- Changes to how Black can be configured -->
diff --git a/src/black/lines.py b/src/black/lines.py
index 2a41db173d4..0d09a6d6507 100644
--- a/src/black/lines.py
+++ b/src/black/lines.py
@@ -446,8 +446,12 @@ def is_complex_subscript(self, leaf: Leaf) -> bool:
 
             if subscript_start.type == syms.subscriptlist:
                 subscript_start = child_towards(subscript_start, leaf)
+
+        test_decendants = TEST_DESCENDANTS
+        if Preview.walrus_subscript in self.mode:
+            test_decendants.add(syms.namedexpr_test)
         return subscript_start is not None and any(
-            n.type in TEST_DESCENDANTS for n in subscript_start.pre_order()
+            n.type in test_decendants for n in subscript_start.pre_order()
         )
 
     def enumerate_with_length(
diff --git a/tests/data/cases/preview_pep_572.py b/tests/data/cases/preview_pep_572.py
index 8e801ff6cdc..75ad0cc4176 100644
--- a/tests/data/cases/preview_pep_572.py
+++ b/tests/data/cases/preview_pep_572.py
@@ -3,5 +3,5 @@
 x[:(a:=0)]
 
 # output
-x[(a := 0):]
-x[:(a := 0)]
+x[(a := 0) :]
+x[: (a := 0)]