Merge branch '3.12' of https://github.com/python/cpython into 3.12

Lib/colorsys.py

@@ -83,7 +83,7 @@ def rgb_to_hls(r, g, b):
     if l <= 0.5:
         s = rangec / sumc
     else:
-        s = rangec / (2.0-sumc)
+        s = rangec / (2.0-maxc-minc)  # Not always 2.0-sumc: gh-106498.
     rc = (maxc-r) / rangec
     gc = (maxc-g) / rangec
     bc = (maxc-b) / rangec

Lib/test/test_colorsys.py

@@ -69,6 +69,16 @@ def test_hls_values(self):
             self.assertTripleEqual(hls, colorsys.rgb_to_hls(*rgb))
             self.assertTripleEqual(rgb, colorsys.hls_to_rgb(*hls))
 
+    def test_hls_nearwhite(self):  # gh-106498
+        values = (
+            # rgb, hls: these do not work in reverse
+            ((0.9999999999999999, 1, 1), (0.5, 1.0, 1.0)),
+            ((1, 0.9999999999999999, 0.9999999999999999), (0.0, 1.0, 1.0)),
+        )
+        for rgb, hls in values:
+            self.assertTripleEqual(hls, colorsys.rgb_to_hls(*rgb))
+            self.assertTripleEqual((1.0, 1.0, 1.0), colorsys.hls_to_rgb(*hls))
+
     def test_yiq_roundtrip(self):
         for r in frange(0.0, 1.0, 0.2):
             for g in frange(0.0, 1.0, 0.2):

Misc/NEWS.d/next/Library/2023-07-11-09-25-40.gh-issue-106530.VgXrMx.rst

@@ -0,0 +1,2 @@
+Revert a change to :func:`colorsys.rgb_to_hls` that caused division by zero
+for certain almost-white inputs.  Patch by Terry Jan Reedy.