Make ListedColormap.monochrome a property #29125
Merged
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The calculated property replaces the attribute monochome, which was manually set on
__init__
, but was not correctly set for all possible inputs.This property ensures consistency and simplifies initialization at the cost of some computation overhead to determine whether the colormap is monochrome.
The computation cost is bearable (even without caching), because it's only used in
ContourSet._process_colors
.It's a separate discussion whether we need this property on colormaps at all (at least as public API). Usually, colormaps are not monochrome and monochrome colormaps are a very special edge case used in contours only. We may eventually deprecate it, but since it is currently public API, let's leave it for now.
There's also a technical API incompatibility in that users cannot set the attribute anymore, but I'd argue that that has never been intended and there's no practical use-case, so I refrain from the extra hassle of allowing setting this property.