Added type hints

Tests/test_imageops.py

@@ -606,7 +606,7 @@ def test_autocontrast_preserve_one_color(color: tuple[int, int, int]) -> None:
     assert_image_equal(img, out)
 
 
-def test_dither_primary_returns_image():
+def test_dither_primary_returns_image() -> None:
     im = Image.new("RGB", (4, 4), (128, 128, 128))
     out = ImageOps.dither_primary(im)
 
@@ -615,20 +615,25 @@ def test_dither_primary_returns_image():
     assert out.mode == "RGB"
 
 
-def test_dither_primary_uses_only_primary_colors():
+def test_dither_primary_uses_only_primary_colors() -> None:
     im = Image.new("RGB", (4, 4), (200, 100, 50))
     out = ImageOps.dither_primary(im)
 
-    pixels = out.load()
+    px = out.load()
+    assert px is not None
+
     for x in range(out.width):
         for y in range(out.height):
-            r, g, b = pixels[x, y]
+            value = px[x, y]
+            assert isinstance(value, tuple)
+
+            r, g, b = value
             assert r in (0, 255)
             assert g in (0, 255)
             assert b in (0, 255)
 
 
-def test_dither_primary_small_image():
+def test_dither_primary_small_image() -> None:
     im = Image.new("RGB", (2, 2), (255, 0, 0))
     out = ImageOps.dither_primary(im)
 

src/PIL/ImageOps.py

@@ -675,9 +675,12 @@ def dither_primary(image: Image.Image) -> Image.Image:
     dst = out.load()
 
     # Step 1: primary color reduction
+    assert src is not None
     for x in range(width):
         for y in range(height):
-            r, g, b = src[x, y]
+            px = src[x, y]
+            assert isinstance(px, tuple)
+            r, g, b = px
             src[x, y] = (
                 255 if r > 127 else 0,
                 255 if g > 127 else 0,
@@ -685,6 +688,7 @@ def dither_primary(image: Image.Image) -> Image.Image:
             )
 
     # Step 2: ordered dithering (2x2 blocks)
+    assert dst is not None
     for x in range(0, width - 1, 2):
         for y in range(0, height - 1, 2):
             p1 = src[x, y]
@@ -692,18 +696,22 @@ def dither_primary(image: Image.Image) -> Image.Image:
             p3 = src[x + 1, y]
             p4 = src[x + 1, y + 1]
 
+            assert isinstance(p1, tuple)
+            assert isinstance(p2, tuple)
+            assert isinstance(p3, tuple)
+            assert isinstance(p4, tuple)
             red = (p1[0] + p2[0] + p3[0] + p4[0]) / 4
             green = (p1[1] + p2[1] + p3[1] + p4[1]) / 4
             blue = (p1[2] + p2[2] + p3[2] + p4[2]) / 4
 
-            r = [_dither_saturation(red, q) for q in range(4)]
-            g = [_dither_saturation(green, q) for q in range(4)]
-            b = [_dither_saturation(blue, q) for q in range(4)]
+            r1 = [_dither_saturation(red, q) for q in range(4)]
+            g1 = [_dither_saturation(green, q) for q in range(4)]
+            b1 = [_dither_saturation(blue, q) for q in range(4)]
 
-            dst[x, y] = (r[0], g[0], b[0])
-            dst[x, y + 1] = (r[1], g[1], b[1])
-            dst[x + 1, y] = (r[2], g[2], b[2])
-            dst[x + 1, y + 1] = (r[3], g[3], b[3])
+            dst[x, y] = (r1[0], g1[0], b1[0])
+            dst[x, y + 1] = (r1[1], g1[1], b1[1])
+            dst[x + 1, y] = (r1[2], g1[2], b1[2])
+            dst[x + 1, y + 1] = (r1[3], g1[3], b1[3])
 
     return out