FIX: return static view of good/bad/under

Otherwise we will hand a view back to the user and it will change
under them if `set_under` (e.g.) is called.

Author: tacaswell

lib/matplotlib/colors.py

@@ -652,7 +652,7 @@ def get_bad(self):
         """Get the color for masked values."""
         if not self._isinit:
             self._init()
-        return self._lut[self._i_bad]
+        return np.array(self._lut[self._i_bad])
 
     def set_bad(self, color='k', alpha=None):
         """Set the color for masked values."""
@@ -665,7 +665,7 @@ def get_under(self):
         """Get the color for low out-of-range values."""
         if not self._isinit:
             self._init()
-        return self._lut[self._i_under]
+        return np.array(self._lut[self._i_under])
 
     def set_under(self, color='k', alpha=None):
         """Set the color for low out-of-range values."""
@@ -678,7 +678,7 @@ def get_over(self):
         """Get the color for high out-of-range values."""
         if not self._isinit:
             self._init()
-        return self._lut[self._i_over]
+        return np.array(self._lut[self._i_over])
 
     def set_over(self, color='k', alpha=None):
         """Set the color for high out-of-range values."""

lib/matplotlib/tests/test_colors.py

@@ -1187,6 +1187,16 @@ def test_get_under_over_bad():
     assert_array_equal(cmap.get_bad(), cmap(np.nan))
 
 
+@pytest.mark.parametrize('kind', ('over', 'under', 'bad'))
+def test_non_mutable_get_values(kind):
+    cmap = copy.copy(plt.get_cmap('viridis'))
+    init_value = getattr(cmap, f'get_{kind}')()
+    getattr(cmap, f'set_{kind}')('k')
+    black_value = getattr(cmap, f'get_{kind}')()
+    assert np.all(black_value == [0, 0, 0, 1])
+    assert not np.all(init_value == black_value)
+
+
 def test_colormap_alpha_array():
     cmap = plt.get_cmap('viridis')
     vals = [-1, 0.5, 2]  # under, valid, over