Black's treatment of trailing commas depends on previous statements.

[JohnADawson]

Black's treatment of trailing commas depends on previous statements.

[JelleZijlstra]

I believe this is because a trailing comma in this context is only legal in 3.6+. If you use an f-string, we know the file is 3.6+, so we can use other 3.6+ syntax.

However, Python 3.5 is long dead. We can probably get rid of this behavior now.

[JohnADawson]

@JelleZijlstra, as your explanation predicts, running

black --diff --target-version=py312 file0.py 

produces

--- file0.py	2024-07-13 21:54:24.113436+00:00
+++ file0.py	2024-07-13 22:52:31.502265+00:00
@@ -10,7 +10,7 @@
     "were",
     "Peter,",
     "Susan,",
     "Edmund",
     "and",
-    "Lucy."
+    "Lucy.",
 )
would reformat file0.py

All done! ✨ 🍰 ✨
1 file would be reformatted.