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Fix legend labelcolor=‘linecolor’ to handle various corner cases, e.g. step histograms and transparent markers #30328

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Fix legend labelcolor=‘linecolor’ to handle various corner cases, e.g. step histograms and transparent markers #30328

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dabaf62
add tests for various corner cases of legends with `labelcolor` set t…
lukashergt Jul 18, 2025
335e76e
fix legends with `labelcolor` set to `linecolor`: change ordering fro…
lukashergt Jul 18, 2025
8d9555e
account for the `classic` style in the mpl tests; need to specify `no…
lukashergt Jul 18, 2025
0fc6fbe
remove unnecessary `loc=1` in new tests for `labelcolor_linecolor`
lukashergt Jul 18, 2025
db46a5c
use `mpl.colors.same_color` also for the `none` checks
lukashergt Jul 18, 2025
64e3a86
Apply suggestions from code review
lukashergt Jul 18, 2025
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22 changes: 17 additions & 5 deletions lib/matplotlib/legend.py
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Original file line number Diff line number Diff line change
Expand Up @@ -576,7 +576,11 @@ def __init__(
# set the text color

color_getters = { # getter function depends on line or patch
'linecolor': ['get_color', 'get_facecolor'],
'linecolor': ['get_markerfacecolor',
'get_facecolor',
'get_markeredgecolor',
'get_edgecolor',
'get_color'],
'markerfacecolor': ['get_markerfacecolor', 'get_facecolor'],
'mfc': ['get_markerfacecolor', 'get_facecolor'],
'markeredgecolor': ['get_markeredgecolor', 'get_edgecolor'],
Expand All @@ -596,18 +600,26 @@ def __init__(
try:
color = getattr(handle, getter_name)()
if isinstance(color, np.ndarray):
if (
color.shape[0] == 1
or np.isclose(color, color[0]).all()
if color.size == 0:
continue
elif (
color.shape[0] == 1
or np.isclose(color, color[0]).all()
):
text.set_color(color[0])
else:
pass
elif cbook._str_lower_equal(color, 'none'):
continue
elif mpl.colors.to_rgba(color)[3] == 0:
continue
else:
text.set_color(color)
break
except AttributeError:
pass
continue
else:
text.set_color('none')
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If I understand correctly this is executed as a fallback if color could not be detected. Then, it feels wrong to set full transparency, because it makes the text invisible. I think we should rather leave the default as we did before.

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@lukashergt lukashergt Jul 18, 2025 •
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Yes, this is a fallback for the case that fc, ec, and c all have continue-ed through, i.e. they are either of the following:

  • an empty array,
  • 'none' or 'None',
  • colour with zero alpha value,
  • AttributeError raised on the getter function.

Otherwise they would have broken (note the break statement) out of the loop beforehand, in which case the else case of the for ... else ... construction won't get invoked.

Final example case from the test_legend_labelcolor_linecolor_plot test:

import numpy as np
import matplotlib.pyplot as plt
x = np.arange(5)
fig, ax = plt.subplots()
p = ax.plot(x, 'o', c='none', mec='none', label="invisible circles with invisible label")
leg = ax.legend(labelcolor='linecolor')
image

So yes, the label entry is invisible because the markers and the legend handle are also invisible. In this stand-alone example this seems nonsensical, but something of this sort might come in handy when trying to insert a dummy legend entry in-between other legend entries for spacing.

elif cbook._str_equal(labelcolor, 'none'):
for text in self.texts:
text.set_color(labelcolor)
Expand Down
238 changes: 238 additions & 0 deletions lib/matplotlib/tests/test_legend.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1068,6 +1068,244 @@ def test_legend_labelcolor_rcparam_markerfacecolor_short():
assert mpl.colors.same_color(text.get_color(), color)


def test_legend_labelcolor_linecolor_histograms():
x = np.arange(10)

# testing c kwarg for bar, step, and stepfilled histograms
fig, ax = plt.subplots()
_, _, h = ax.hist(x, histtype='bar', color='r',
label="red bar hist with a red label")
leg = ax.legend(labelcolor='linecolor')
tc = leg.texts[0].get_color()
assert mpl.colors.same_color(tc, 'r')
assert mpl.colors.same_color(tc, leg.get_patches()[0].get_facecolor())
assert mpl.colors.same_color(tc, h[0].get_facecolor())

fig, ax = plt.subplots()
_, _, h = ax.hist(x, histtype='step', color='g',
label="green step hist with a green label")
leg = ax.legend(labelcolor='linecolor')
tc = leg.texts[0].get_color()
assert mpl.colors.same_color(tc, 'g')
assert mpl.colors.same_color(tc, leg.get_patches()[0].get_edgecolor())
assert mpl.colors.same_color(tc, h[0].get_edgecolor())

fig, ax = plt.subplots()
_, _, h = ax.hist(x, histtype='stepfilled', color='b',
label="blue stepfilled hist with a blue label")
leg = ax.legend(labelcolor='linecolor')
tc = leg.texts[0].get_color()
assert mpl.colors.same_color(tc, 'b')
assert mpl.colors.same_color(tc, leg.get_patches()[0].get_facecolor())
assert mpl.colors.same_color(tc, h[0].get_facecolor())

# testing c, fc, and ec combinations for bar histograms
fig, ax = plt.subplots()
_, _, h = ax.hist(x, histtype='bar', color='r', ec='b',
label="red bar hist with blue edges and a red label")
leg = ax.legend(labelcolor='linecolor')
tc = leg.texts[0].get_color()
assert mpl.colors.same_color(tc, 'r')
assert mpl.colors.same_color(tc, leg.get_patches()[0].get_facecolor())
assert mpl.colors.same_color(tc, h[0].get_facecolor())

fig, ax = plt.subplots()
_, _, h = ax.hist(x, histtype='bar', fc='r', ec='b',
label="red bar hist with blue edges and a red label")
leg = ax.legend(labelcolor='linecolor')
tc = leg.texts[0].get_color()
assert mpl.colors.same_color(tc, 'r')
assert mpl.colors.same_color(tc, leg.get_patches()[0].get_facecolor())
assert mpl.colors.same_color(tc, h[0].get_facecolor())

fig, ax = plt.subplots()
_, _, h = ax.hist(x, histtype='bar', fc='none', ec='b',
label="unfilled blue bar hist with a blue label")
leg = ax.legend(labelcolor='linecolor')
tc = leg.texts[0].get_color()
assert mpl.colors.same_color(tc, 'b')
assert mpl.colors.same_color(tc, leg.get_patches()[0].get_edgecolor())
assert mpl.colors.same_color(tc, h[0].get_edgecolor())

# testing c, and ec combinations for step histograms
fig, ax = plt.subplots()
_, _, h = ax.hist(x, histtype='step', color='r', ec='b',
label="blue step hist with a blue label")
leg = ax.legend(labelcolor='linecolor')
tc = leg.texts[0].get_color()
assert mpl.colors.same_color(tc, 'b')
assert mpl.colors.same_color(tc, leg.get_patches()[0].get_edgecolor())
assert mpl.colors.same_color(tc, h[0].get_edgecolor())

fig, ax = plt.subplots()
_, _, h = ax.hist(x, histtype='step', ec='b',
label="blue step hist with a blue label")
leg = ax.legend(labelcolor='linecolor')
tc = leg.texts[0].get_color()
assert mpl.colors.same_color(tc, 'b')
assert mpl.colors.same_color(tc, leg.get_patches()[0].get_edgecolor())
assert mpl.colors.same_color(tc, h[0].get_edgecolor())

# testing c, fc, and ec combinations for stepfilled histograms
fig, ax = plt.subplots()
_, _, h = ax.hist(x, histtype='stepfilled', color='r', ec='b',
label="red stepfilled hist, blue edges, red label")
leg = ax.legend(labelcolor='linecolor')
tc = leg.texts[0].get_color()
assert mpl.colors.same_color(tc, 'r')
assert mpl.colors.same_color(tc, leg.get_patches()[0].get_facecolor())
assert mpl.colors.same_color(tc, h[0].get_facecolor())

fig, ax = plt.subplots()
_, _, h = ax.hist(x, histtype='stepfilled', fc='r', ec='b',
label="red stepfilled hist, blue edges, red label")
leg = ax.legend(labelcolor='linecolor')
tc = leg.texts[0].get_color()
assert mpl.colors.same_color(tc, 'r')
assert mpl.colors.same_color(tc, leg.get_patches()[0].get_facecolor())
assert mpl.colors.same_color(tc, h[0].get_facecolor())

fig, ax = plt.subplots()
_, _, h = ax.hist(x, histtype='stepfilled', fc='none', ec='b',
label="unfilled blue stepfilled hist, blue label")
leg = ax.legend(labelcolor='linecolor')
tc = leg.texts[0].get_color()
assert mpl.colors.same_color(tc, 'b')
assert mpl.colors.same_color(tc, leg.get_patches()[0].get_edgecolor())
assert mpl.colors.same_color(tc, h[0].get_edgecolor())

fig, ax = plt.subplots()
_, _, h = ax.hist(x, histtype='stepfilled', fc='r', ec='none',
label="edgeless red stepfilled hist with a red label")
leg = ax.legend(labelcolor='linecolor')
tc = leg.texts[0].get_color()
assert mpl.colors.same_color(tc, 'r')
assert mpl.colors.same_color(tc, leg.get_patches()[0].get_facecolor())
assert mpl.colors.same_color(tc, h[0].get_facecolor())
plt.close('all')


def test_legend_labelcolor_linecolor_plot():
x = np.arange(5)

# testing line plot
fig, ax = plt.subplots()
p = ax.plot(x, c='r', label="red line with a red label")
leg = ax.legend(labelcolor='linecolor')
tc = leg.texts[0].get_color()
assert mpl.colors.same_color(tc, 'r')
assert mpl.colors.same_color(tc, leg.get_lines()[0].get_color())
assert mpl.colors.same_color(tc, p[0].get_color())

# testing c, fc, and ec combinations for maker plots
fig, ax = plt.subplots()
p = ax.plot(x, 'o', c='r', label="red circles with a red label")
leg = ax.legend(labelcolor='linecolor')
tc = leg.texts[0].get_color()
assert mpl.colors.same_color(tc, 'r')
assert mpl.colors.same_color(tc, leg.get_lines()[0].get_color())
assert mpl.colors.same_color(tc, p[0].get_color())

fig, ax = plt.subplots()
p = ax.plot(x, 'o', c='r', mec='b', label="red circles, blue edges, red label")
leg = ax.legend(labelcolor='linecolor')
tc = leg.texts[0].get_color()
assert mpl.colors.same_color(tc, 'r')
assert mpl.colors.same_color(tc, leg.get_lines()[0].get_color())
assert mpl.colors.same_color(tc, p[0].get_color())

fig, ax = plt.subplots()
p = ax.plot(x, 'o', mfc='r', mec='b', label="red circles, blue edges, red label")
leg = ax.legend(labelcolor='linecolor')
tc = leg.texts[0].get_color()
assert mpl.colors.same_color(tc, 'r')
assert mpl.colors.same_color(tc, leg.get_lines()[0].get_markerfacecolor())
assert mpl.colors.same_color(tc, p[0].get_markerfacecolor())

# 'none' cases
fig, ax = plt.subplots()
p = ax.plot(x, 'o', mfc='none', mec='b', label="blue unfilled circles, blue label")
leg = ax.legend(labelcolor='linecolor')
tc = leg.texts[0].get_color()
assert mpl.colors.same_color(tc, 'b')
assert mpl.colors.same_color(tc, leg.get_lines()[0].get_markeredgecolor())
assert mpl.colors.same_color(tc, p[0].get_markeredgecolor())

fig, ax = plt.subplots()
p = ax.plot(x, 'o', mfc='r', mec='none', label="red edgeless circles, red label")
leg = ax.legend(labelcolor='linecolor')
tc = leg.texts[0].get_color()
assert mpl.colors.same_color(tc, 'r')
assert mpl.colors.same_color(tc, leg.get_lines()[0].get_markerfacecolor())
assert mpl.colors.same_color(tc, p[0].get_markerfacecolor())

fig, ax = plt.subplots()
p = ax.plot(x, 'o', c='none', mec='none', label="invisible circles and label")
leg = ax.legend(labelcolor='linecolor')
tc = leg.texts[0].get_color()
assert mpl.colors.same_color(tc, 'none')
assert mpl.colors.same_color(tc, leg.get_lines()[0].get_markerfacecolor())
assert mpl.colors.same_color(tc, leg.get_lines()[0].get_markeredgecolor())
assert mpl.colors.same_color(tc, leg.get_lines()[0].get_color())
assert mpl.colors.same_color(tc, p[0].get_markerfacecolor())
assert mpl.colors.same_color(tc, p[0].get_markeredgecolor())
assert mpl.colors.same_color(tc, p[0].get_color())
plt.close('all')


def test_legend_labelcolor_linecolor_scatter():
x = np.arange(5)

# testing c, fc, and ec combinations for scatter plots
fig, ax = plt.subplots()
p = ax.scatter(x, x, c='r', label="red circles with a red label")
leg = ax.legend(labelcolor='linecolor')
tc = leg.texts[0].get_color()
assert mpl.colors.same_color(tc, 'r')
assert mpl.colors.same_color(tc, leg.legend_handles[0].get_facecolor())
assert mpl.colors.same_color(tc, p.get_facecolor())

fig, ax = plt.subplots()
p = ax.scatter(x, x, c='r', ec='b', label="red circles, blue edges, red label")
leg = ax.legend(labelcolor='linecolor')
tc = leg.texts[0].get_color()
assert mpl.colors.same_color(tc, 'r')
assert mpl.colors.same_color(tc, leg.legend_handles[0].get_facecolor())
assert mpl.colors.same_color(tc, p.get_facecolor())

fig, ax = plt.subplots()
p = ax.scatter(x, x, fc='r', ec='b', label="red circles, blue edges, red label")
leg = ax.legend(labelcolor='linecolor')
tc = leg.texts[0].get_color()
assert mpl.colors.same_color(tc, 'r')
assert mpl.colors.same_color(tc, leg.legend_handles[0].get_facecolor())
assert mpl.colors.same_color(tc, p.get_facecolor())

# 'none' cases
fig, ax = plt.subplots()
p = ax.scatter(x, x, fc='none', ec='b', label="blue unfilled circles, blue label")
leg = ax.legend(labelcolor='linecolor')
tc = leg.texts[0].get_color()
assert mpl.colors.same_color(tc, 'b')
assert mpl.colors.same_color(tc, leg.legend_handles[0].get_edgecolor())
assert mpl.colors.same_color(tc, p.get_edgecolor())

fig, ax = plt.subplots()
p = ax.scatter(x, x, fc='r', ec='none', label="red edgeless circles, red label")
leg = ax.legend(labelcolor='linecolor')
tc = leg.texts[0].get_color()
assert mpl.colors.same_color(tc, 'r')
assert mpl.colors.same_color(tc, leg.legend_handles[0].get_facecolor())
assert mpl.colors.same_color(tc, p.get_facecolor())

fig, ax = plt.subplots()
p = ax.scatter(x, x, c='none', ec='none', label="invisible circles and label")
leg = ax.legend(labelcolor='linecolor')
tc = leg.texts[0].get_color()
assert mpl.colors.same_color(tc, 'none')
plt.close('all')


@pytest.mark.filterwarnings("ignore:No artists with labels found to put in legend")
def test_get_set_draggable():
legend = plt.legend()
Expand Down
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