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Change Locator MAXTICKS checking to emitting a log at WARNING level. #13510

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merged 1 commit into from
Sep 5, 2019
Merged

Change Locator MAXTICKS checking to emitting a log at WARNING level. #13510

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6 changes: 6 additions & 0 deletions doc/api/next_api_changes/2019-02-25-AL.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,6 @@
API changes
```````````

When more than `.Locator.MAXTICKS` ticks are generated, the behavior of
`.Locator.raise_if_exceeds` changed from raising a RuntimeError to emitting a
log at WARNING level.
14 changes: 10 additions & 4 deletions lib/matplotlib/tests/test_dates.py
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Expand Up @@ -135,12 +135,13 @@ def test_date_axvline():
fig.autofmt_xdate()


def test_too_many_date_ticks():
def test_too_many_date_ticks(caplog):
# Attempt to test SF 2715172, see
# https://sourceforge.net/tracker/?func=detail&aid=2715172&group_id=80706&atid=560720
# setting equal datetimes triggers and expander call in
# transforms.nonsingular which results in too many ticks in the
# DayLocator. This should trigger a Locator.MAXTICKS RuntimeError
# DayLocator. This should emit a log at WARNING level.
caplog.set_level("WARNING")
t0 = datetime.datetime(2000, 1, 20)
tf = datetime.datetime(2000, 1, 20)
fig = plt.figure()
Expand All @@ -152,8 +153,13 @@ def test_too_many_date_ticks():
'Attempting to set identical left == right' in str(rec[0].message)
ax.plot([], [])
ax.xaxis.set_major_locator(mdates.DayLocator())
with pytest.raises(RuntimeError):
fig.savefig('junk.png')
fig.canvas.draw()
# The warning is emitted multiple times because the major locator is also
# called both when placing the minor ticks (for overstriking detection) and
# during tick label positioning.
assert caplog.records and all(
record.name == "matplotlib.ticker" and record.levelname == "WARNING"
for record in caplog.records)


@image_comparison(['RRuleLocator_bounds.png'])
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18 changes: 14 additions & 4 deletions lib/matplotlib/ticker.py
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Expand Up @@ -1690,11 +1690,21 @@ def __call__(self):
raise NotImplementedError('Derived must override')

def raise_if_exceeds(self, locs):
"""Raise a RuntimeError if ``len(locs) > self.MAXTICKS``."""
"""
Log at WARNING level if *locs* is longer than `Locator.MAXTICKS`.

This is intended to be called immediately before returning *locs* from
``__call__`` to inform users in case their Locator returns a huge
number of ticks, causing Matplotlib to run out of memory.

The "strange" name of this method dates back to when it would raise an
exception instead of emitting a log.
"""
if len(locs) >= self.MAXTICKS:
raise RuntimeError("Locator attempting to generate {} ticks from "
"{} to {}: exceeds Locator.MAXTICKS".format(
len(locs), locs[0], locs[-1]))
_log.warning(
"Locator attempting to generate %s ticks ([%s, ..., %s]), "
"which exceeds Locator.MAXTICKS (%s).",
len(locs), locs[0], locs[-1], self.MAXTICKS)
return locs

def nonsingular(self, v0, v1):
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