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[Bug]: colors.LinearSegmentedColormap.from_list does not take two tuples in 3.8.0 #26949

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dave-shirley-faraday opened this issue Sep 28, 2023 · 3 comments · Fixed by #26952
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[Bug]: colors.LinearSegmentedColormap.from_list does not take two tuples in 3.8.0 #26949

dave-shirley-faraday opened this issue Sep 28, 2023 · 3 comments · Fixed by #26952
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status: confirmed bug
Milestone
v3.8.1

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@dave-shirley-faraday
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dave-shirley-faraday commented Sep 28, 2023 •
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Bug summary

Incrementing from v3.7 to v3.8 the option to specify a start and end value is no longer functioning when two values are specified. It still works when three are specified.

## This works:
matplotlib.colors.LinearSegmentedColormap.from_list("myMap", ["#000000", "#FFFFFF"])

## This does not:
matplotlib.colors.LinearSegmentedColormap.from_list("myMap", [(0,"#000000"), (1,"#FFFFFF")])

Code for reproduction

matplotlib.colors.LinearSegmentedColormap.from_list("myMap", [(0,"#000000"), (1,"#FFFFFF")])

Actual outcome

Traceback (most recent call last):
File "", line 1, in
File "/Users/dave/.local/share/virtualenvs/projects-t0xU6-ce/lib/python3.10/site-packages/matplotlib/colors.py", line 1065, in from_list
colors : array-like of colors or array-like of (value, color)
File "/Users/dave/.local/share/virtualenvs/projects-t0xU6-ce/lib/python3.10/site-packages/matplotlib/colors.py", line 489, in to_rgba_array
pass
ValueError: '#000000' is not a valid color value.

Expected outcome

<matplotlib.colors.LinearSegmentedColormap object at 0x101e7f520>

Additional information

Worked in 3.7

The issue I think is related to zipped values being passed to r, g, b, a = to_rgba_array(colors).T. A tuple gets passed in rather than a list.

## tuple len 2 fails
>>> matplotlib.colors.to_rgba_array(("#000000", "#FFFFFF"))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/dave/.local/share/virtualenvs/model_train-t0xU6-ce/lib/python3.10/site-packages/matplotlib/colors.py", line 489, in to_rgba_array
    pass
ValueError: '#000000' is not a valid color value.
## list works
>>> matplotlib.colors.to_rgba_array(["#000000", "#FFFFFF"])
array([[0., 0., 0., 1.],
       [1., 1., 1., 1.]])

Changing r, g, b, a = to_rgba_array(colors).T in colors.py:LinearSegmentedColormap.from_list to r, g, b, a = to_rgba_array(list(colors)).T or similar may fix.

Operating system

OS/X

Matplotlib Version

3.8.0

Matplotlib Backend

MacOSX

Python version

Python 3.10.9

Jupyter version

No response

Installation

None
@rcomer
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rcomer commented Sep 28, 2023 •
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Thanks for the report and the debugging notes @dave-shirley-faraday. This bisects to #24691.

@rcomer rcomer added this to the v3.8.1 milestone Sep 28, 2023
@rcomer
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rcomer commented Sep 28, 2023 •
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This seems to depend on whether to_rgba gets a list or a tuple:

In [10]: to_rgba_array(["#000000", "#FFFFFF"])
Out[10]: 
array([[0., 0., 0., 1.],
       [1., 1., 1., 1.]])

In [11]: to_rgba_array(("#000000", "#FFFFFF"))
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
Cell In[11], line 1
----> 1 to_rgba_array(("#000000", "#FFFFFF"))

File ~/git_stuff/matplotlib/lib/matplotlib/colors.py:489, in to_rgba_array(c, alpha)
    487         raise e
    488 if isinstance(c, str):
--> 489     raise ValueError(f"{c!r} is not a valid color value.")
    491 if len(c) == 0:
    492     return np.zeros((0, 4), float)

ValueError: '#000000' is not a valid color value.

Edit: sorry, I see you already said that!

@rcomer rcomer mentioned this issue Sep 28, 2023
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@dave-shirley-faraday
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dave-shirley-faraday commented Sep 28, 2023 •
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Yes I think with the new parameterization of to_rgba the tuple ("#000000", "#FFFFFF") is now treated as (c, alpha) rather than (c, c), where hex values are not valid color values (it expects 'red' or similar). Perhaps detecting the color type (eg checking for a leading #) in to_rgba might fix.

[edit] Yup, looks like your PR should address

@rcomer rcomer mentioned this issue Oct 8, 2023
Closed
facundolucianna added a commit to FIUBA-Posgrado-Inteligencia-Artificial/intro_ia that referenced this issue May 11, 2024
@facundolucianna
Hotfix for matplotlib3.8.0 bug matplotlib/matplotlib#26949
18addf0
facundolucianna added a commit to FIUBA-Posgrado-Inteligencia-Artificial/aprMaqI_CEIA that referenced this issue May 11, 2024
@facundolucianna
Hotfix for matplotlib3.8.0 bug matplotlib/matplotlib#26949
0519860
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FIX 2-tuple of colors in to_rgba_array rcomer/matplotlib
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@rcomer @dave-shirley-faraday