8000 [Bug]: to_rgba_array("none") returns empty array · Issue #28475 · matplotlib/matplotlib · GitHub
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[Bug]: to_rgba_array("none") returns empty array #28475

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story645 opened this issue Jun 27, 2024 · 3 comments
Open

[Bug]: to_rgba_array("none") returns empty array #28475

story645 opened this issue Jun 27, 2024 · 3 comments
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topic: color/color & colormaps topic: testing

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@story645
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story645 commented Jun 27, 2024 •
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Bug summary

mcolors.to_rgba_array("none") returns an empty array while mcolors.to_rgba("none") and mcolors.to_rgba_array(["none"]) return (0,0,0,0) (which is the documented value of None) and this leads to inconsistencies when trying to use mcolors.same_color

Actual outcome

>>> import matplotlib.colors as mcolors
>>> mcolors.to_rgba("none")
(0.0, 0.0, 0.0, 0.0)
>>> mcolors.to_rgba_array("none") 
array([], shape=(0, 4), dtype=float64)
>>> mcolors.to_rgba_array(["none"])
array([[0., 0., 0., 0.]])
>>> mcolors.same_color("none", mcolors.to_rgba("none"))
False
>>> mcolors.same_color(["none"], mcolors.to_rgba("none")) 
True

Expected outcome

>>> import matplotlib.colors as mcolors
>>> mcolors.to_rgba("none")
(0.0, 0.0, 0.0, 0.0)
>>> mcolors.to_rgba_array("none") 
array([[0., 0., 0., 0.]])
>>> mcolors.to_rgba_array(["none"])
array([[0., 0., 0., 0.]])
>>> mcolors.same_color("none", mcolors.to_rgba("none"))
True
>>> mcolors.same_color(["none"], mcolors.to_rgba("none")) 
True

Additional information

I tried the quick fixes of changing the return here to array([[0., 0., 0., 0.]]) and np.array([to_rgba('none')], float)

matplotlib/lib/matplotlib/colors.py

Lines 482 to 483 in d347c32

if cbook._str_lower_equal(c, "none"):
return np.zeros((0, 4), float)

That yielded a ton of test failures, mostly around colorbars/contours, hatches, and but roughly the diffs all looked something like this:

contourf_extend_patches (actual, expected)
image

colorbar_two_slope
image

Also I realize this could be not worth fixing and a quick fix is to cast none to a list in same_color
@Impaler343 Impaler343 mentioned this issue Jun 27, 2024
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@story645
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story645 commented Aug 12, 2024 •
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Someone at scipy tracked this down to being an issue w/ eager conversion to color that relies on 'none'/empty array for if statements to preserve the correct alpha values. xref #28710

@story645 story645 mentioned this issue Nov 15, 2024
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@story645 story645 mentioned this issue Feb 5, 2025
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@story645 story645 mentioned this issue Mar 9, 2025
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@rcomer
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rcomer commented Mar 9, 2025

The existing behaviour is clearly deliberate but I agree with @story645 about what I expected to happen. Is it worth adding a boolean parameter so you could choose between the two behaviours?

@story645
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story645 commented Mar 9, 2025

Is it worth adding a boolean parameter so you could choose between the two behaviours?

I've been thinking of a sort of true constant for none, but flagging would probably do the same trick - what I'm thinking is that it could be really useful to know which parts of the codebase need the empty behavior.

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