ListedColormap: repeat colors if necessary (#147)

* ListedColormap: repeat colors if necessary

* changelog

Author: mathause

CHANGELOG.md

@@ -40,6 +40,11 @@
 
 - Ensure the current axes (`plt.gca()`) is not changed by calling `mpu.colorbar(...)` ([#136](https://github.com/mathause/mplotutils/pull/136)).
 
+### Internal changes
+
+- Align internal usage of `ListedColormaps` with changes in [matplotlib/matplotlib#29135](https://github.com/matplotlib/matplotlib/pull/29135)
+  ([#145](https://github.com/mathause/mplotutils/pull/145), and [#147](https://github.com/mathause/mplotutils/pull/147)).
+
 ## v0.5.0 (27.03.2024)
 
 Version v0.5.0 aligns passing multiple axes to `colorbar` with matplotlib.

mplotutils/_colormaps.py

@@ -1,3 +1,5 @@
+import itertools
+
 import matplotlib as mpl
 import numpy as np
 from matplotlib.colors import from_levels_and_colors
@@ -54,7 +56,8 @@ def _color_palette(cmap, n_colors):
 
     colors_i = np.linspace(0, 1.0, n_colors)
     if isinstance(cmap, (list, tuple)):
-        # we have a list of colors
+        # expand or truncate the list of colors to n_colors
+        cmap = list(itertools.islice(itertools.cycle(cmap), n_colors))
         cmap = ListedColormap(cmap)
         pal = cmap(colors_i)
     elif isinstance(cmap, str):

mplotutils/tests/test_colormap.py

@@ -77,8 +77,25 @@ def test_from_levels_and_cmap_seaborn_cmap():
 
 
 def test_from_levels_and_cmap_colorstring():
-    pytest.importorskip("seaborn")
 
     levels = [1, 2, 3]
     cmap, norm = mpu.from_levels_and_cmap(levels, "0.1")
     assert_cmap_norm(cmap, norm, levels, extend="neither")
+
+    np.testing.assert_equal(cmap.colors[0], np.array([0.1, 0.1, 0.1, 1.0]))
+    np.testing.assert_equal(cmap.colors[1], np.array([0.1, 0.1, 0.1, 1.0]))
+
+
+def test_from_levels_and_cmap_color_list_explicit():
+
+    levels = [1, 2, 3, 4, 5]
+
+    # ensure colors are repeated (although that can also be unexpected)
+    cmap, norm = mpu.from_levels_and_cmap(levels, ["b", "k"])
+
+    assert_cmap_norm(cmap, norm, levels, extend="neither")
+
+    np.testing.assert_equal(cmap.colors[0], np.array([0.0, 0.0, 1.0, 1.0]))  # blue
+    np.testing.assert_equal(cmap.colors[1], np.array([0.0, 0.0, 0.0, 1.0]))  # black
+    np.testing.assert_equal(cmap.colors[2], np.array([0.0, 0.0, 1.0, 1.0]))  # blue
+    np.testing.assert_equal(cmap.colors[3], np.array([0.0, 0.0, 0.0, 1.0]))  # black