Added Color.categorical_set that generates a creates a list of visually distinct colors

src/build123d/geometry.py

@@ -34,6 +34,7 @@ from __future__ import annotations
 # other pylint warning to temp remove:
 #   too-many-arguments, too-many-locals, too-many-public-methods,
 #   too-many-statements, too-many-instance-attributes, too-many-branches
+import colorsys
 import copy as copy_module
 import itertools
 import json
@@ -1345,6 +1346,74 @@ class Color:
         """Color repr"""
         return f"Color{str(tuple(self))}"
 
+    @classmethod
+    def categorical_set(
+        cls,
+        color_count: int,
+        starting_hue: ColorLike | float = 0.0,
+        alpha: float | Iterable[float] = 1.0,
+    ) -> list[Color]:
+        """Generate a palette of evenly spaced colors.
+
+        Creates a list of visually distinct colors suitable for representing
+        discrete categories (such as different parts, assemblies, or data
+        series). Colors are evenly spaced around the hue circle and share
+        consistent lightness and saturation levels, resulting in balanced
+        perceptual contrast across all hues.
+
+        Produces palettes similar in appearance to the **Tableau 10** and **D3
+        Category10** color sets—both widely recognized standards in data
+        visualization for their clarity and accessibility. These values have
+        been empirically chosen to maintain consistent perceived brightness
+        across hues while avoiding overly vivid or dark colors.
+
+        Args:
+            color_count (int): Number of colors to generate.
+            starting_hue (ColorLike | float): Either a Color-like object or
+                a hue value in the range [0.0, 1.0] that defines the starting color.
+            alpha (float | Iterable[float]): Alpha value(s) for the colors. Can be a
+                single float or an iterable of length `color_count`.
+
+        Returns:
+            list[Color]: List of generated colors.
+
+        Raises:
+            ValueError: If starting_hue is out of range or alpha length mismatch.
+        """
+
+        # --- Determine starting hue ---
+        if isinstance(starting_hue, float):
+            if not (0.0 <= starting_hue <= 1.0):
+                raise ValueError("Starting hue must be within range 0.0–1.0")
+        elif isinstance(starting_hue, int):
+            if starting_hue < 0:
+                raise ValueError("Starting color integer must be non-negative")
+            rgb = tuple(Color(starting_hue))[:3]
+            starting_hue = colorsys.rgb_to_hls(*rgb)[0]
+        else:
+            raise TypeError(
+                "Starting hue must be a float in [0,1] or an integer color literal"
+            )
+
+        # --- Normalize alpha values ---
+        if isinstance(alpha, (float, int)):
+            alphas = [float(alpha)] * color_count
+        else:
+            alphas = list(alpha)
+            if len(alphas) != color_count:
+                raise ValueError("Number of alpha values must match color_count")
+
+        # --- Generate color list ---
+        hues = np.linspace(
+            starting_hue, starting_hue + 1.0, color_count, endpoint=False
+        )
+        colors = [
+            cls(*colorsys.hls_to_rgb(h % 1.0, 0.55, 0.9), a)
+            for h, a in zip(hues, alphas)
+        ]
+
+        return colors
+
     @staticmethod
     def _rgb_from_int(triplet: int) -> tuple[float, float, float]:
         red, remainder = divmod(triplet, 256**2)

tests/test_direct_api/test_color.py

@@ -26,8 +26,9 @@ license:
 
 """
 
+import colorsys
 import copy
-
+import math
 import numpy as np
 import pytest
 
@@ -36,44 +37,84 @@ from build123d.geometry import Color
 
 
 # Overloads
-@pytest.mark.parametrize("color, expected", [
+@pytest.mark.parametrize(
+    "color, expected",
+    [
         pytest.param(Color("blue"), (0, 0, 1, 1), id="name"),
         pytest.param(Color("blue", alpha=0.5), (0, 0, 1, 0.5), id="name + kw alpha"),
         pytest.param(Color("blue", 0.5), (0, 0, 1, 0.5), id="name + alpha"),
-])
+    ],
+)
 def test_overload_name(color, expected):
     np.testing.assert_allclose(tuple(color), expected, 1e-5)
 
-@pytest.mark.parametrize("color, expected", [
+
+@pytest.mark.parametrize(
+    "color, expected",
+    [
         pytest.param(Color(0.0, 1.0, 0.0), (0, 1, 0, 1), id="rgb"),
         pytest.param(Color(1.0, 1.0, 0.0, 0.5), (1, 1, 0, 0.5), id="rgba"),
-    pytest.param(Color(1.0, 1.0, 0.0, alpha=0.5), (1, 1, 0, 0.5), id="rgb + kw alpha"),
+        pytest.param(
-    pytest.param(Color(red=0.1, green=0.2, blue=0.3, alpha=0.5), (0.1, 0.2, 0.3, 0.5), id="kw rgba"),
+            Color(1.0, 1.0, 0.0, alpha=0.5), (1, 1, 0, 0.5), id="rgb + kw alpha"
-])
+        ),
+        pytest.param(
+            Color(red=0.1, green=0.2, blue=0.3, alpha=0.5),
+            (0.1, 0.2, 0.3, 0.5),
+            id="kw rgba",
+        ),
+    ],
+)
 def test_overload_rgba(color, expected):
     np.testing.assert_allclose(tuple(color), expected, 1e-5)
 
-@pytest.mark.parametrize("color, expected", [
+
-    pytest.param(Color(0x996692), (0x99 / 0xFF, 0x66 / 0xFF, 0x92 / 0xFF, 1), id="color_code"),
+@pytest.mark.parametrize(
-    pytest.param(Color(0x006692, 0x80), (0, 0x66 / 0xFF, 0x92 / 0xFF, 0x80 / 0xFF), id="color_code + alpha"),
+    "color, expected",
-    pytest.param(Color(0x006692, alpha=0x80), (0, 102 / 255, 146 / 255, 128 / 255), id="color_code + kw alpha"),
+    [
-    pytest.param(Color(color_code=0x996692, alpha=0xCC), (153 / 255, 102 / 255, 146 / 255, 204 / 255), id="kw color_code + alpha"),
+        pytest.param(
-])
+            Color(0x996692), (0x99 / 0xFF, 0x66 / 0xFF, 0x92 / 0xFF, 1), id="color_code"
+        ),
+        pytest.param(
+            Color(0x006692, 0x80),
+            (0, 0x66 / 0xFF, 0x92 / 0xFF, 0x80 / 0xFF),
+            id="color_code + alpha",
+        ),
+        pytest.param(
+            Color(0x006692, alpha=0x80),
+            (0, 102 / 255, 146 / 255, 128 / 255),
+            id="color_code + kw alpha",
+        ),
+        pytest.param(
+            Color(color_code=0x996692, alpha=0xCC),
+            (153 / 255, 102 / 255, 146 / 255, 204 / 255),
+            id="kw color_code + alpha",
+        ),
+    ],
+)
 def test_overload_hex(color, expected):
     np.testing.assert_allclose(tuple(color), expected, 1e-5)
 
-@pytest.mark.parametrize("color, expected", [
+
+@pytest.mark.parametrize(
+    "color, expected",
+    [
         pytest.param(Color((0.1,)), (0.1, 1.0, 1.0, 1.0), id="tuple r"),
         pytest.param(Color((0.1, 0.2)), (0.1, 0.2, 1.0, 1.0), id="tuple rg"),
         pytest.param(Color((0.1, 0.2, 0.3)), (0.1, 0.2, 0.3, 1.0), id="tuple rgb"),
-    pytest.param(Color((0.1, 0.2, 0.3, 0.4)), (0.1, 0.2, 0.3, 0.4), id="tuple rbga"),
+        pytest.param(
+            Color((0.1, 0.2, 0.3, 0.4)), (0.1, 0.2, 0.3, 0.4), id="tuple rbga"
+        ),
         pytest.param(Color((0.1, 0.2, 0.3, 0.4)), (0.1, 0.2, 0.3, 0.4), id="kw tuple"),
-])
+    ],
+)
 def test_overload_tuple(color, expected):
     np.testing.assert_allclose(tuple(color), expected, 1e-5)
 
+
 # ColorLikes
-@pytest.mark.parametrize("color_like", [
+@pytest.mark.parametrize(
+    "color_like",
+    [
         pytest.param(Quantity_ColorRGBA(1, 0, 0, 1), id="Quantity_ColorRGBA"),
         pytest.param("red", id="name str"),
         pytest.param("red ", id="name str whitespace"),
@@ -86,7 +127,9 @@ def test_overload_tuple(color, expected):
         pytest.param("#ff0000ff", id="hex str rgba 24bit"),
         pytest.param(" #ff0000ff ", id="hex str rgba 24bit whitespace"),
         pytest.param(("#ff0000ff",), id="tuple hex str rgba 24bit"),
-    pytest.param(("#ff0000ff", .6), id="tuple hex str rgba 24bit + alpha (not used)"),
+        pytest.param(
+            ("#ff0000ff", 0.6), id="tuple hex str rgba 24bit + alpha (not used)"
+        ),
         pytest.param("#f00", id="hex str rgb 12bit"),
         pytest.param(" #f00 ", id="hex str rgb 12bit whitespace"),
         pytest.param(("#f00",), id="tuple hex str rgb 12bit"),
@@ -94,47 +137,59 @@ def test_overload_tuple(color, expected):
         pytest.param("#f00f", id="hex str rgba 12bit"),
         pytest.param(" #f00f ", id="hex str rgba 12bit whitespace"),
         pytest.param(("#f00f",), id="tuple hex str rgba 12bit"),
-    pytest.param(("#f00f", .6), id="tuple hex str rgba 12bit + alpha (not used)"),
+        pytest.param(("#f00f", 0.6), id="tuple hex str rgba 12bit + alpha (not used)"),
-    pytest.param(0xff0000, id="hex int"),
+        pytest.param(0xFF0000, id="hex int"),
-    pytest.param((0xff0000), id="tuple hex int"),
+        pytest.param((0xFF0000), id="tuple hex int"),
-    pytest.param((0xff0000, 0xff), id="tuple hex int + alpha"),
+        pytest.param((0xFF0000, 0xFF), id="tuple hex int + alpha"),
         pytest.param((1, 0, 0), id="tuple rgb int"),
         pytest.param((1, 0, 0, 1), id="tuple rgba int"),
-    pytest.param((1., 0., 0.), id="tuple rgb float"),
+        pytest.param((1.0, 0.0, 0.0), id="tuple rgb float"),
-    pytest.param((1., 0., 0., 1.), id="tuple rgba float"),
+        pytest.param((1.0, 0.0, 0.0, 1.0), id="tuple rgba float"),
-])
+    ],
+)
 def test_color_likes(color_like):
     expected = (1, 0, 0, 1)
     np.testing.assert_allclose(tuple(Color(color_like)), expected, 1e-5)
     np.testing.assert_allclose(tuple(Color(color_like=color_like)), expected, 1e-5)
 
-@pytest.mark.parametrize("color_like, expected", [
+
+@pytest.mark.parametrize(
+    "color_like, expected",
+    [
         pytest.param(Color(), (1, 1, 1, 1), id="empty Color()"),
-    pytest.param(1., (1, 1, 1, 1), id="r float"),
+        pytest.param(1.0, (1, 1, 1, 1), id="r float"),
-    pytest.param((1.,), (1, 1, 1, 1), id="tuple r float"),
+        pytest.param((1.0,), (1, 1, 1, 1), id="tuple r float"),
-    pytest.param((1., 0.), (1, 0, 1, 1), id="tuple rg float"),
+        pytest.param((1.0, 0.0), (1, 0, 1, 1), id="tuple rg float"),
-])
+    ],
+)
 def test_color_likes_incomplete(color_like, expected):
     np.testing.assert_allclose(tuple(Color(color_like)), expected, 1e-5)
     np.testing.assert_allclose(tuple(Color(color_like=color_like)), expected, 1e-5)
 
-@pytest.mark.parametrize("color_like", [
+
+@pytest.mark.parametrize(
+    "color_like",
+    [
         pytest.param(Quantity_ColorRGBA(1, 0, 0, 0.6), id="Quantity_ColorRGBA"),
         pytest.param(("red", 0.6), id="tuple name str + alpha"),
         pytest.param(("#ff0000", 0.6), id="tuple hex str rgb 24bit + alpha"),
         pytest.param(("#ff000099"), id="tuple hex str rgba 24bit"),
         pytest.param(("#f00", 0.6), id="tuple hex str rgb 12bit + alpha"),
         pytest.param(("#f009"), id="tuple hex str rgba 12bit"),
-    pytest.param((0xff0000, 153), id="tuple hex int + alpha int"),
+        pytest.param((0xFF0000, 153), id="tuple hex int + alpha int"),
-    pytest.param((1., 0., 0., 0.6), id="tuple rbga float"),
+        pytest.param((1.0, 0.0, 0.0, 0.6), id="tuple rbga float"),
-])
+    ],
+)
 def test_color_likes_alpha(color_like):
     expected = (1, 0, 0, 0.6)
     np.testing.assert_allclose(tuple(Color(color_like)), expected, 1e-5)
     np.testing.assert_allclose(tuple(Color(color_like=color_like)), expected, 1e-5)
 
+
 # Exceptions
-@pytest.mark.parametrize("name", [
+@pytest.mark.parametrize(
+    "name",
+    [
         pytest.param("build123d", id="invalid color name"),
         pytest.param("#ffg", id="invalid rgb 12bit"),
         pytest.param("#fffg", id="invalid rgba 12bit"),
@@ -144,21 +199,34 @@ def test_color_likes_alpha(color_like):
         pytest.param("#fffff", id="short rgb 24bit"),
         pytest.param("#fffffff", id="short rgba 24bit"),
         pytest.param("#fffffffff", id="long rgba 24bit"),
-])
+    ],
+)
 def test_exceptions_color_name(name):
     with pytest.raises(Exception):
         Color(name)
 
-@pytest.mark.parametrize("color_type", [
+
-    pytest.param((dict({"name": "red", "alpha": 1},)), id="dict arg"),
+@pytest.mark.parametrize(
+    "color_type",
+    [
+        pytest.param(
+            (
+                dict(
+                    {"name": "red", "alpha": 1},
+                )
+            ),
+            id="dict arg",
+        ),
         pytest.param(("red", "blue"), id="str + str"),
-    pytest.param((1., "blue"), id="float + str order"),
+        pytest.param((1.0, "blue"), id="float + str order"),
         pytest.param((1, "blue"), id="int + str order"),
-])
+    ],
+)
 def test_exceptions_color_type(color_type):
     with pytest.raises(Exception):
         Color(*color_type)
 
+
 # Methods
 def test_rgba_wrapped():
     c = Color(1.0, 1.0, 0.0, 0.5)
@@ -167,17 +235,87 @@ def test_rgba_wrapped():
     assert c.wrapped.GetRGB().Blue() == 0.0
     assert c.wrapped.Alpha() == 0.5
 
+
 def test_copy():
     c = Color(0.1, 0.2, 0.3, alpha=0.4)
     c_copy = copy.copy(c)
     np.testing.assert_allclose(tuple(c_copy), (0.1, 0.2, 0.3, 0.4), rtol=1e-5)
 
+
 def test_str_repr_is():
     c = Color(1, 0, 0)
     assert str(c) == "Color: (1.0, 0.0, 0.0, 1.0) is 'RED'"
     assert repr(c) == "Color(1.0, 0.0, 0.0, 1.0)"
 
+
 def test_str_repr_near():
     c = Color(1, 0.5, 0)
     assert str(c) == "Color: (1.0, 0.5, 0.0, 1.0) near 'DARKGOLDENROD1'"
     assert repr(c) == "Color(1.0, 0.5, 0.0, 1.0)"
+
+
+class TestColorCategoricalSet:
+    def test_returns_expected_number_of_colors(self):
+        colors = Color.categorical_set(5)
+        assert len(colors) == 5
+        assert all(isinstance(c, Color) for c in colors)
+
+    def test_colors_are_evenly_spaced_in_hue(self):
+        count = 8
+        colors = Color.categorical_set(count)
+        hues = [colorsys.rgb_to_hls(*tuple(c)[:3])[0] for c in colors]
+        diffs = [(hues[(i + 1) % count] - hues[i]) % 1.0 for i in range(count)]
+        avg_diff = sum(diffs) / len(diffs)
+        assert all(math.isclose(d, avg_diff, rel_tol=1e-2) for d in diffs)
+
+    def test_starting_hue_as_float(self):
+        (r, g, b, _) = tuple(Color.categorical_set(1, starting_hue=0.25)[0])
+        h = colorsys.rgb_to_hls(r, g, b)[0]
+        assert math.isclose(h, 0.25, rel_tol=0.05)
+
+    def test_starting_hue_as_int_hex(self):
+        # Blue (0x0000FF) should be valid and return a Color
+        c = Color.categorical_set(1, starting_hue=0x0000FF)[0]
+        assert isinstance(c, Color)
+
+    def test_starting_hue_invalid_type(self):
+        with pytest.raises(TypeError):
+            Color.categorical_set(3, starting_hue="invalid")
+
+    def test_starting_hue_out_of_range(self):
+        with pytest.raises(ValueError):
+            Color.categorical_set(3, starting_hue=1.5)
+        with pytest.raises(ValueError):
+            Color.categorical_set(3, starting_hue=-0.1)
+
+    def test_starting_hue_negative_int(self):
+        with pytest.raises(ValueError):
+            Color.categorical_set(3, starting_hue=-1)
+
+    def test_constant_alpha_applied(self):
+        colors = Color.categorical_set(3, alpha=0.7)
+        for c in colors:
+            (_, _, _, a) = tuple(c)
+            assert math.isclose(a, 0.7, rel_tol=1e-6)
+
+    def test_iterable_alpha_applied(self):
+        alphas = (0.1, 0.5, 0.9)
+        colors = Color.categorical_set(3, alpha=alphas)
+        for a, c in zip(alphas, colors):
+            (_, _, _, returned_alpha) = tuple(c)
+            assert math.isclose(a, returned_alpha, rel_tol=1e-6)
+
+    def test_iterable_alpha_length_mismatch(self):
+        with pytest.raises(ValueError):
+            Color.categorical_set(4, alpha=[0.5, 0.7])
+
+    def test_hues_wrap_around(self):
+        colors = Color.categorical_set(10, starting_hue=0.95)
+        hues = [colorsys.rgb_to_hls(*tuple(c)[:3])[0] for c in colors]
+        assert all(0.0 <= h <= 1.0 for h in hues)
+
+    def test_alpha_defaults_to_one(self):
+        colors = Color.categorical_set(4)
+        for c in colors:
+            (_, _, _, a) = tuple(c)
+            assert math.isclose(a, 1.0, rel_tol=1e-6)