diff --git a/galleries/examples/text_labels_and_annotations/custom_legends.py b/galleries/examples/text_labels_and_annotations/custom_legends.py
index f1714a21a481..18ace0513228 100644
--- a/galleries/examples/text_labels_and_annotations/custom_legends.py
+++ b/galleries/examples/text_labels_and_annotations/custom_legends.py
@@ -28,6 +28,7 @@
# 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
@@ -35,10 +36,10 @@
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:
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
index 0fcabac8c7c0..8ed6e10770e8 100644
--- a/lib/matplotlib/axes/_axes.py
+++ b/lib/matplotlib/axes/_axes.py
@@ -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 an empty legend being drawn.
**2. Explicitly listing the artists and labels in the legend**
diff --git a/lib/matplotlib/legend.py b/lib/matplotlib/legend.py
index 58e5dfcfe3b8..fa43a31d7c17 100644
--- a/lib/matplotlib/legend.py
+++ b/lib/matplotlib/legend.py
@@ -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.")
diff --git a/lib/matplotlib/tests/test_legend.py b/lib/matplotlib/tests/test_legend.py
index 3a35b4051c71..5a64df78fbc9 100644
--- a/lib/matplotlib/tests/test_legend.py
+++ b/lib/matplotlib/tests/test_legend.py
@@ -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()
@@ -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()
@@ -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})
@@ -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
@@ -1071,6 +1072,7 @@ def test_legend_labelcolor_rcparam_markerfacecolor_short():
assert mpl.colors.same_color(text.get_color(), color)
+@pytest.mark.filterwarnings("ignore:No artists with labels found to put in legend")
def test_get_set_draggable():
legend = plt.legend()
assert not legend.get_draggable()
@@ -1289,74 +1291,75 @@ 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 string, 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():
@@ -1375,3 +1378,16 @@ 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, match="No artists with labels found"):
+ plt.legend()
+
+
+@pytest.mark.filterwarnings("ignore:No artists with labels found to put in legend")
+def test_legend_nolabels_draw():
+ plt.plot([1, 2, 3])
+ plt.legend()
+ assert plt.gca().get_legend() is not None
diff --git a/lib/matplotlib/tests/test_pickle.py b/lib/matplotlib/tests/test_pickle.py
index e222a495e437..cab412bff561 100644
--- a/lib/matplotlib/tests/test_pickle.py
+++ b/lib/matplotlib/tests/test_pickle.py
@@ -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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