8000 ENH: Change logging to warning when creating a legend with no labels by Jacob-Stevens-Haas · Pull Request #27172 · matplotlib/matplotlib · GitHub
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ENH: Change logging to warning when creating a legend with no labels #27172

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Merged
merged 7 commits into from
Dec 1, 2023
Merged

ENH: Change logging to warning when creating a legend with no labels #27172

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46286fa
ENH: Change logging to warning when creating a legend with no labels
Jacob-Stevens-Haas Oct 23, 2023
f53b9d9
TST: Add mock labels to mock data.
Jacob-Stevens-Haas Oct 23, 2023
a413a02
DOC: Note warning in legend() documentation
Jacob-Stevens-Haas Oct 24, 2023
bc1054b
DOC: Correct examples to no longer raise UserWarning
Jacob-Stevens-Haas Oct 24, 2023
9f80d55
TST: Add test for drawing empty legend()
Jacob-Stevens-Haas Oct 24, 2023
04e0ceb
TST: Test legend for specific warning when no labels present
Jacob-Stevens-Haas Oct 27, 2023
dbe82fe
TST: Filter no labels warning by message.
Jacob-Stevens-Haas Nov 30, 2023
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5 changes: 3 additions & 2 deletions galleries/examples/text_labels_and_annotations/custom_legends.py
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10000
Original file line number Diff line number Diff line change
Expand Up @@ -28,17 +28,18 @@
# Fixing random state for reproducibility
np.random.seed(19680801)

# %%
N = 10
data = (np.geomspace(1, 10, 100) + np.random.randn(N, 100)).T
cmap = plt.cm.coolwarm
mpl.rcParams['axes.prop_cycle'] = cycler(color=cmap(np.linspace(0, 1, N)))

fig, ax = plt.subplots()
lines = ax.plot(data)
ax.legend()

# %%
# Note that no legend entries were created.
# Since the data does not have any labels, creating a legend requires
# us to define the icons and labels.
# In this case, we can compose a legend using Matplotlib objects that aren't
# explicitly tied to the data that was plotted. For example:

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4 changes: 2 additions & 2 deletions lib/matplotlib/axes/_axes.py
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Expand Up @@ -239,8 +239,8 @@ def legend(self, *args, **kwargs):
selection by using a label starting with an underscore, "_".
A string starting with an underscore is the default label for all
artists, so calling `.Axes.legend` without any arguments and
without setting the labels manually will result in no legend being
drawn.
without setting the labels manually will result in a ``UserWarning``
and no legend being drawn.


**2. Explicitly listing the artists and labels in the legend**
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2 changes: 1 addition & 1 deletion lib/matplotlib/legend.py
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Expand Up @@ -1358,7 +1358,7 @@ def _parse_legend_args(axs, *args, handles=None, labels=None, **kwargs):
elif len(args) == 0: # 0 args: automatically detect labels and handles.
handles, labels = _get_legend_handles_labels(axs, handlers)
if not handles:
log.warning(
_api.warn_external(
"No artists with labels found to put in legend. Note that "
"artists whose label start with an underscore are ignored "
"when legend() is called with no argument.")
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82 changes: 45 additions & 37 deletions lib/matplotlib/tests/test_legend.py
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Expand Up @@ -636,6 +636,7 @@ def test_handler_numpoints():
def test_text_nohandler_warning():
"""Test that Text artists with labels raise a warning"""
fig, ax = plt.subplots()
ax.plot([0], label="mock data")
ax.text(x=0, y=0, s="text", label="label")
with pytest.warns(UserWarning) as record:
ax.legend()
Expand Down Expand Up @@ -703,7 +704,7 @@ def test_legend_title_empty():
# it comes back as an empty string, and that it is not
# visible:
fig, ax = plt.subplots()
ax.plot(range(10))
ax.plot(range(10), label="mock data")
leg = ax.legend()
assert leg.get_title().get_text() == ""
assert not leg.get_title().get_visible()
Expand Down Expand Up @@ -736,7 +737,7 @@ def test_window_extent_cached_renderer():

def test_legend_title_fontprop_fontsize():
# test the title_fontsize kwarg
plt.plot(range(10))
plt.plot(range(10), label="mock data")
with pytest.raises(ValueError):
plt.legend(title='Aardvark', title_fontsize=22,
title_fontproperties={'family': 'serif', 'size': 22})
Expand All @@ -747,27 +748,27 @@ def test_legend_title_fontprop_fontsize():

fig, axes = plt.subplots(2, 3, figsize=(10, 6))
axes = axes.flat
axes[0].plot(range(10))
axes[0].plot(range(10), label="mock data")
leg0 = axes[0].legend(title='Aardvark', title_fontsize=22)
assert leg0.get_title().get_fontsize() == 22
axes[1].plot(range(10))
axes[1].plot(range(10), label="mock data")
leg1 = axes[1].legend(title='Aardvark',
title_fontproperties={'family': 'serif', 'size': 22})
assert leg1.get_title().get_fontsize() == 22
axes[2].plot(range(10))
axes[2].plot(range(10), label="mock data")
mpl.rcParams['legend.title_fontsize'] = None
leg2 = axes[2].legend(title='Aardvark',
title_fontproperties={'family': 'serif'})
assert leg2.get_title().get_fontsize() == mpl.rcParams['font.size']
axes[3].plot(range(10))
axes[3].plot(range(10), label="mock data")
leg3 = axes[3].legend(title='Aardvark')
assert leg3.get_title().get_fontsize() == mpl.rcParams['font.size']
axes[4].plot(range(10))
axes[4].plot(range(10), label="mock data")
mpl.rcParams['legend.title_fontsize'] = 20
leg4 = axes[4].legend(title='Aardvark',
title_fontproperties={'family': 'serif'})
assert leg4.get_title().get_fontsize() == 20
axes[5].plot(range(10))
axes[5].plot(range(10), label="mock data")
leg5 = axes[5].legend(title='Aardvark')
assert leg5.get_title().get_fontsize() == 20

Expand Down Expand Up @@ -1072,7 +1073,7 @@ def test_legend_labelcolor_rcparam_markerfacecolor_short():


def test_get_set_draggable():
legend = plt.legend()
legend = plt.legend(labels=["mock data"])
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@timhoffm timhoffm Nov 13, 2023 •
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I'm somewhat uneasy about this pattern of providing labels when there is no data.

  1. Passing labels only is supported but discouraged.
  2. While currently supported, it feels, that passing more labels than we have data should possibly warn as well. At least it's non-sensical. - But that'd be a separate PR. For here, we should just not use this pattern.

I suggest to silence the warning explicitly rather than through a sketchy code construct: Decorate the function with

@pytest.mark.filterwarnings("ignore:No artists with labels found to put in legend")

instead.

Also in the following test functions.

assert not legend.get_draggable()
legend.set_draggable(True)
assert legend.get_draggable()
Expand Down Expand Up @@ -1289,74 +1290,75 @@ def test_loc_invalid_tuple_exception():
fig, ax = plt.subplots()
with pytest.raises(ValueError, match=('loc must be string, coordinate '
'tuple, or an integer 0-10, not \\(1.1,\\)')):
ax.legend(loc=(1.1, ))
ax.legend(loc=(1.1, ), labels=["mock data"])

with pytest.raises(ValueError, match=('loc must be string, coordinate '
'tuple, or an integer 0-10, not \\(0.481, 0.4227, 0.4523\\)')):
ax.legend(loc=(0.481, 0.4227, 0.4523))
ax.legend(loc=(0.481, 0.4227, 0.4523), labels=["mock data"])

with pytest.raises(ValueError, match=('loc must be string, coordinate '
'tuple, or an integer 0-10, not \\(0.481, \'go blue\'\\)')):
ax.legend(loc=(0.481, "go blue"))
ax.legend(loc=(0.481, "go blue"), labels=["mock data"])


def test_loc_valid_tuple():
fig, ax = plt.subplots()
ax.legend(loc=(0.481, 0.442))
ax.legend(loc=(1, 2))
ax.legend(loc=(0.481, 0.442), labels=["mock data"])
ax.legend(loc=(1, 2), labels=["mock data"])


def test_loc_valid_list():
fig, ax = plt.subplots()
ax.legend(loc=[0.481, 0.442])
ax.legend(loc=[1, 2])
ax.legend(loc=[0.481, 0.442], labels=["mock data"])
ax.legend(loc=[1, 2], labels=["mock data"])


def test_loc_invalid_list_exception():
fig, ax = plt.subplots()
with pytest.raises(ValueError, match=('loc must be string, coordinate '
'tuple, or an integer 0-10, not \\[1.1, 2.2, 3.3\\]')):
ax.legend(loc=[1.1, 2.2, 3.3])
ax.legend(loc=[1.1, 2.2, 3.3], labels=["mock data"])


def test_loc_invalid_type():
fig, ax = plt.subplots()
with pytest.raises(ValueError, match=("loc must be string, coordinate "
"tuple, or an integer 0-10, not {'not': True}")):
ax.legend(loc={'not': True})
ax.legend(loc={'not': True}, labels=["mock data"])


def test_loc_validation_numeric_value():
fig, ax = plt.subplots()
ax.legend(loc=0)
ax.legend(loc=1)
ax.legend(loc=5)
ax.legend(loc=10)
ax.legend(loc=0, labels=["mock data"])
ax.legend(loc=1, labels=["mock data"])
ax.legend(loc=5, labels=["mock data"])
ax.legend(loc=10, labels=["mock data"])
with pytest.raises(ValueError, match=('loc must be stri 1E0A ng, coordinate '
'tuple, or an integer 0-10, not 11')):
ax.legend(loc=11)
ax.legend(loc=11, labels=["mock data"])

with pytest.raises(ValueError, match=('loc must be string, coordinate '
'tuple, or an integer 0-10, not -1')):
ax.legend(loc=-1)
ax.legend(loc=-1, labels=["mock data"])


def test_loc_validation_string_value():
fig, ax = plt.subplots()
ax.legend(loc='best')
ax.legend(loc='upper right')
ax.legend(loc='best')
ax.legend(loc='upper right')
ax.legend(loc='upper left')
ax.legend(loc='lower left')
ax.legend(loc='lower right')
ax.legend(loc='right')
ax.legend(loc='center left')
ax.legend(loc='center right')
ax.legend(loc='lower center')
ax.legend(loc='upper center')
labels = ["mock data"]
ax.legend(loc='best', labels=labels)
ax.legend(loc='upper right', labels=labels)
ax.legend(loc='best', labels=labels)
ax.legend(loc='upper right', labels=labels)
ax.legend(loc='upper left', labels=labels)
ax.legend(loc='lower left', labels=labels)
ax.legend(loc='lower right', labels=labels)
ax.legend(loc='right', labels=labels)
ax.legend(loc='center left', labels=labels)
ax.legend(loc='center right', labels=labels)
ax.legend(loc='lower center', labels=labels)
ax.legend(loc='upper center', labels=labels)
with pytest.raises(ValueError, match="'wrong' is not a valid value for"):
ax.legend(loc='wrong')
ax.legend(loc='wrong', labels=labels)


def test_legend_handle_label_mismatch():
Expand All @@ -1375,3 +1377,9 @@ def test_legend_handle_label_mismatch_no_len():
labels=iter(["pl1", "pl2", "pl3"]))
assert len(legend.legend_handles) == 2
assert len(legend.get_texts()) == 2


def test_legend_nolabels_warning():
plt.plot([1, 2, 3])
with pytest.raises(UserWarning):
plt.legend()
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Let's at least make sure, a legend is created and attached to the Axes:

Suggested change
plt.legend()
plt.legend()
assert plt.gca().get_legend() is not None

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Gotcha, makes sense! In addition, is pattern you suggested above of @pytest.mark.filterwarnings(...) preferable to warnings.catch_warnings()+simplefilter pattern?

2 changes: 1 addition & 1 deletion lib/matplotlib/tests/test_pickle.py
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Expand Up @@ -90,7 +90,7 @@ def _generate_complete_test_figure(fig_ref):
plt.legend(loc='upper left')

plt.subplot(3, 3, 9)
plt.errorbar(x, x * -0.5, xerr=0.2, yerr=0.4)
plt.errorbar(x, x * -0.5, xerr=0.2, yerr=0.4, label='$-.5 x$')
plt.legend(draggable=True)

fig_ref.align_ylabels() # Test handling of _align_label_groups Groupers.
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