API: add a check that we have at least one region

tacaswell · tacaswell · commit 64fff76d3157 · 2020-07-03T18:32:20.000-04:00
diff --git a/lib/matplotlib/colors.py b/lib/matplotlib/colors.py
@@ -1470,6 +1470,9 @@ def __init__(self, boundaries, ncolors, clip=False, *, extend='neither'):
         self.vmax = boundaries[-1]
         self.boundaries = np.asarray(boundaries)
         self.N = len(self.boundaries)
+        if self.N < 2:
+            raise ValueError("You must provide at least 2 boundaries "
+                             f"(1 region) but you passed in {boundaries!r}")
         self.Ncmap = ncolors
         self.extend = extend
 
