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Small error in docstring of matplotlib.colors.from_levels_and_colors #27188

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glthm opened this issue Oct 25, 2023 · 3 comments · Fixed by #27189
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Small error in docstring of matplotlib.colors.from_levels_and_colors #27188

glthm opened this issue Oct 25, 2023 · 3 comments · Fixed by #27189
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Documentation: API files in lib/ and doc/api Documentation Good first issue Open a pull request against these issues if there are no active ones!
Milestone
v3.8.1

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@glthm
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glthm commented Oct 25, 2023

matplotlib/lib/matplotlib/colors.py

Lines 2708 to 2762 in 3958242

def from_levels_and_colors(levels, colors, extend='neither'):
"""
A helper routine to generate a cmap and a norm instance which
behave similar to contourf's levels and colors arguments.
Parameters
----------
levels : sequence of numbers
The quantization levels used to construct the `BoundaryNorm`.
Value ``v`` is quantized to level ``i`` if ``lev[i] <= v < lev[i+1]``.
colors : sequence of colors
The fill color to use for each level. If *extend* is "neither" there
must be ``n_level - 1`` colors. For an *extend* of "min" or "max" add
one extra color, and for an *extend* of "both" add two colors.
extend : {'neither', 'min', 'max', 'both'}, optional
The behaviour when a value falls out of range of the given levels.
See `~.Axes.contourf` for details.
Returns
-------
cmap : `~matplotlib.colors.Normalize`
norm : `~matplotlib.colors.Colormap`
"""
slice_map = {
'both': slice(1, -1),
'min': slice(1, None),
'max': slice(0, -1),
'neither': slice(0, None),
}
_api.check_in_list(slice_map, extend=extend)
color_slice = slice_map[extend]
n_data_colors = len(levels) - 1
n_expected = n_data_colors + color_slice.start - (color_slice.stop or 0)
if len(colors) != n_expected:
raise ValueError(
f'With extend == {extend!r} and {len(levels)} levels, '
f'expected {n_expected} colors, but got {len(colors)}')
cmap = ListedColormap(colors[color_slice], N=n_data_colors)
if extend in ['min', 'both']:
cmap.set_under(colors[0])
else:
cmap.set_under('none')
if extend in ['max', 'both']:
cmap.set_over(colors[-1])
else:
cmap.set_over('none')
cmap.colorbar_extend = extend
norm = BoundaryNorm(levels, ncolors=n_data_colors)
return cmap, norm

The docstring of matplotlib.colors.from_levels_and_colors states that the function returns:

    cmap : `~matplotlib.colors.Normalize`
    norm : `~matplotlib.colors.Colormap`

while the code confirms that, as expected, it's the opposite that is returned (cmap is a Colormap and norm is a Normalize)
@rcomer
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rcomer commented Oct 25, 2023

Good spot @glthm! Are you interested in making a pull request to correct it?

@rcomer rcomer added Documentation Documentation: API files in lib/ and doc/api Good first issue Open a pull request against these issues if there are no active ones! labels Oct 25, 2023
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Good first issue - notes for new contributors

This issue is suited to new contributors because it does not require understanding of the Matplotlib internals. To get started, please see our contributing guide.

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@art3xa art3xa mentioned this issue Oct 25, 2023
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@QuLogic QuLogic added this to the v3.8.1 milestone Oct 25, 2023
@glthm
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glthm commented Oct 26, 2023

someone was faster than me, my first pull request won't be for today, maybe next time

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Fix typo in docstring of matplotlib.colors.from_levels_and_colors art3xa/matplotlib
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@QuLogic @rcomer @glthm