Added test for cmap.n_variates == 0 in colorizer

trygvrad · trygvrad · commit 6934853efa9a · 2025-10-29T21:41:10.000+01:00
diff --git a/lib/matplotlib/colorizer.py b/lib/matplotlib/colorizer.py
@@ -766,7 +766,7 @@ def _ensure_norm(norm, n_components=1):
             scale_cls = _api.check_getitem(scale._scale_mapping, norm=norm)
             return _auto_norm_from_scale(scale_cls)()
         return norm
-    else:  # n_components > 1
+    elif n_components > 1:
         if not np.iterable(norm):
             _api.check_isinstance((colors.MultiNorm, None, tuple), norm=norm)
         if norm is None:
@@ -777,6 +777,9 @@ def _ensure_norm(norm, n_components=1):
             return norm
         raise ValueError(
             f"Invalid norm for multivariate colormap with {n_components} inputs")
+    else:  # n_components == 0
+        raise ValueError(
+            "Invalid cmap. A colorizer object must have a cmap with `n_variates` >= 1")
 
 
 def _ensure_cmap(cmap, accept_multivariate=False):
diff --git a/lib/matplotlib/tests/test_colors.py b/lib/matplotlib/tests/test_colors.py
@@ -2199,6 +2199,16 @@ def test_colorizer_multinorm_explicit():
     assert_array_almost_equal(ca.to_rgba(data), res)
 
 
+def test_invalid_cmap_n_components_zero():
+    class CustomColormap(mcolors.Colormap):
+        def __init__(self):
+            super().__init__("custom")
+            self.n_variates = 0
+
+    with pytest.raises(ValueError, match='`n_variates` >= 1'):
+        ca = mcolorizer.Colorizer(CustomColormap())
+
+
 def test_colorizer_bivar_cmap():
     ca = mcolorizer.Colorizer('BiOrangeBlue', [mcolors.Normalize(), 'log'])
 
