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Warn when "best" loc of legend is used with lots of data #12455

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Merged
merged 12 commits into from
Jan 21, 2019
Merged

Warn when "best" loc of legend is used with lots of data #12455

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b30e93b
Warn when "best" loc of legend is used with lots of data
kbrose Oct 9, 2018
cf1d30f
Increase size limit before warning
kbrose Oct 9, 2018
f7be89e
Update data size in test
kbrose Oct 9, 2018
b6e044b
Only warn if best was used by default
kbrose Nov 15, 2018
6bce43f
Add test that no warning is issued when best specified manually
kbrose Nov 15, 2018
504f619
update to new way of warning after rebase
kbrose Nov 15, 2018
7997f4d
Remove unnecessarily copied comment in test
kbrose Nov 15, 2018
0365455
use rc_context, thanks @timhoffm for the tip
kbrose Nov 17, 2018
f01b674
forgot to import rc_context after rebase
kbrose Nov 17, 2018
2cb3550
Incorporate @timhoffm style change
timhoffm Nov 21, 2018
282ac53
Incorporate @timhoffm style change
timhoffm Nov 21, 2018
f89a78c
Some more refactoring courtesy of @timhoffm
kbrose Nov 22, 2018
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13 changes: 12 additions & 1 deletion lib/matplotlib/legend.py
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Original file line number Diff line number Diff line change
Expand Up @@ -484,6 +484,7 @@ def __init__(self, parent, handles, labels,
raise TypeError("Legend needs either Axes or Figure as parent")
self.parent = parent

self._loc_used_default = loc is None
if loc is None:
loc = rcParams["legend.loc"]
if not self.isaxes and loc in [0, 'best']:
Expand Down Expand Up @@ -568,7 +569,10 @@ def __init__(self, parent, handles, labels,
else:
self.get_frame().set_alpha(framealpha)

self._loc = loc
tmp = self._loc_used_default
self._set_loc(loc)
self._loc_used_default = tmp # ignore changes done by _set_loc

# figure out title fontsize:
if title_fontsize is None:
title_fontsize = rcParams['legend.title_fontsize']
Expand All @@ -592,6 +596,7 @@ def _set_loc(self, loc):
# find_offset function will be provided to _legend_box and
# _legend_box will draw itself at the location of the return
# value of the find_offset.
self._loc_used_default = False
self._loc_real = loc
self.stale = True
self._legend_box.set_offset(self._findoffset)
Expand Down Expand Up @@ -1108,6 +1113,12 @@ def _find_best_position(self, width, height, renderer, consider=None):
assert self.isaxes

verts, bboxes, lines, offsets = self._auto_legend_data()
if self._loc_used_default and verts.shape[0] > 200000:
# this size results in a 3+ second render time on a good machine
cbook._warn_external(
'Creating legend with loc="best" can be slow with large '
'amounts of data.'
)

bbox = Bbox.from_bounds(0, 0, width, height)
if consider is None:
Expand Down
26 changes: 26 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 @@ -13,6 +13,7 @@
from matplotlib.legend_handler import HandlerTuple
import matplotlib.legend as mlegend
from matplotlib.cbook.deprecation import MatplotlibDeprecationWarning
from matplotlib import rc_context


def test_legend_ordereddict():
Expand Down Expand Up @@ -563,3 +564,28 @@ def test_alpha_handles():
lh.set_alpha(1.0)
assert lh.get_facecolor()[:-1] == hh[1].get_facecolor()[:-1]
assert lh.get_edgecolor()[:-1] == hh[1].get_edgecolor()[:-1]


def test_warn_big_data_best_loc():
fig, ax = plt.subplots()
ax.plot(np.arange(200001), label='Is this big data?')
with pytest.warns(UserWarning) as records:
with rc_context({'legend.loc': 'best'}):
l = ax.legend()
fig.canvas.draw()
# The _find_best_position method of Legend is called twice, duplicating
# the warning message.
assert len(records) == 2
for record in records:
assert str(record.message) == (
'Creating legend with loc="best" can be slow with large'
' amounts of data.')


def test_no_warn_big_data_when_loc_specified():
fig, ax = plt.subplots()
ax.plot(np.arange(200001), label='Is this big data?')
with pytest.warns(None) as records:
l = ax.legend('best')
fig.canvas.draw()
assert len(records) == 0