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Allow sharing locators across axises. #28429

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Allow sharing locators across axises. #28429

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9 changes: 9 additions & 0 deletions doc/api/next_api_changes/behavior/28429-AL.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,9 @@
Tick locating code now ensure that the locator's axis is correctly set
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Tick locators maintain a reference to the Axis on which they are used (so that
they can e.g. check the size of the Axis to know how many ticks will fit), but
is problematic if the same locator object is used for multiple Axis. From now
on, before calling a locator to determine tick locations, Matplotlib will
ensure that the locator's axis is correctly (temporarily) set to the correct
Axis. This fix can cause a change in behavior if a locator's axis had been
intentionally set to an artificial value.
6 changes: 3 additions & 3 deletions lib/matplotlib/axis.py
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Expand Up @@ -1527,14 +1527,14 @@ def get_ticklines(self, minor=False):

def get_majorticklocs(self):
"""Return this Axis' major tick locations in data coordinates."""
return self.major.locator()
return self.major.locator._call_with_axis(self)

def get_minorticklocs(self):
"""Return this Axis' minor tick locations in data coordinates."""
# Remove minor ticks duplicating major ticks.
minor_locs = np.asarray(self.minor.locator())
minor_locs = np.asarray(self.minor.locator._call_with_axis(self))
if self.remove_overlapping_locs:
major_locs = self.major.locator()
major_locs = self.major.locator._call_with_axis(self)
transform = self._scale.get_transform()
tr_minor_locs = transform.transform(minor_locs)
tr_major_locs = transform.transform(major_locs)
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13 changes: 13 additions & 0 deletions lib/matplotlib/tests/test_ticker.py
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Expand Up @@ -1873,3 +1873,16 @@ def test_minorticks_on_multi_fig():

assert ax.get_xgridlines()
assert isinstance(ax.xaxis.get_minor_locator(), mpl.ticker.AutoMinorLocator)


def test_locator_reuse():
fig = plt.figure()
ax = fig.add_subplot(xlim=(.6, .8))
loc = mticker.AutoLocator()
ax.xaxis.set_major_locator(loc)
ax.yaxis.set_major_locator(loc)
fig.draw_without_rendering()
xticklabels = [l.get_text() for l in ax.get_xticklabels()]
yticklabels = [l.get_text() for l in ax.get_yticklabels()]
assert xticklabels == ["0.60", "0.65", "0.70", "0.75", "0.80"]
assert yticklabels == ["0.0", "0.2", "0.4", "0.6", "0.8", "1.0"]
19 changes: 18 additions & 1 deletion lib/matplotlib/ticker.py
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Expand Up @@ -1629,11 +1629,28 @@
str(type(self)))

def __call__(self):
"""Return the locations of the ticks."""
"""
Return the locations of the ticks.

The returned locations depend on the locator's axis. If a locator
is used across multiple axises, make sure to (temporarily) set
``locator.axis`` to the correct axis before getting the tick locations.
"""
# note: some locators return data limits, other return view limits,
# hence there is no *one* interface to call self.tick_values.
raise NotImplementedError('Derived must override')

def _call_with_axis(self, axis):
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This should get a docstring. If I understand it correctly, we always want to call this method instead of __call__, which then makes the explicit self.axis unused because it is always temporarily overwritten with the passed parameter.

We might choose to make this public as the new API, so people can use it directly (users wanting to evaluate, and locator authors implementing their logic directly here). We could then later deprecate __call__ and self.axis/set_axis.

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Docstring added. Agreed that this should be the future public API, but I didn't want to commit yet to anything.

"""
Get the tick locations while the locator's axis is temporarily set to *axis*.
"""
current = axis
try:
self.set_axis(axis)
return self()
finally:

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lib/matplotlib/ticker.py#L1651 

Added line #L1651 was not covered by tests
self.set_axis(current)

def raise_if_exceeds(self, locs):
"""
Log at WARNING level if *locs* is longer than `Locator.MAXTICKS`.
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20 changes: 12 additions & 8 deletions lib/mpl_toolkits/axisartist/axislines.py
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Expand Up @@ -185,11 +185,11 @@ def get_tick_iterators(self, axes):
angle_normal, angle_tangent = {0: (90, 0), 1: (0, 90)}[self.nth_coord]

major = self.axis.major
major_locs = major.locator()
major_locs = major.locator._call_with_axis(self.axis)
major_labels = major.formatter.format_ticks(major_locs)

minor = self.axis.minor
minor_locs = minor.locator()
minor_locs = minor.locator._call_with_axis(self.axis)
minor_labels = minor.formatter.format_ticks(minor_locs)

tick_to_axes = self.get_tick_transform(axes) - axes.transAxes
Expand Down Expand Up @@ -246,11 +246,11 @@ def get_tick_iterators(self, axes):
angle_normal, angle_tangent = {0: (90, 0), 1: (0, 90)}[self.nth_coord]

major = self.axis.major
major_locs = major.locator()
major_locs = major.locator._call_with_axis(self.axis)
major_labels = major.formatter.format_ticks(major_locs)

minor = self.axis.minor
minor_locs = minor.locator()
minor_locs = minor.locator._call_with_axis(self.axis)
minor_labels = minor.formatter.format_ticks(minor_locs)

data_to_axes = axes.transData - axes.transAxes
Expand Down Expand Up @@ -351,18 +351,22 @@ def get_gridlines(self, which="major", axis="both"):
locs = []
y1, y2 = self.axes.get_ylim()
if which in ("both", "major"):
locs.extend(self.axes.xaxis.major.locator())
locs.extend(
self.axes.xaxis.major.locator._call_with_axis(self.axes.xaxis))
if which in ("both", "minor"):
locs.extend(self.axes.xaxis.minor.locator())
locs.extend(
self.axes.xaxis.minor.locator._call_with_axis(self.axes.xaxis))
gridlines.extend([[x, x], [y1, y2]] for x in locs)

if axis in ("both", "y"):
x1, x2 = self.axes.get_xlim()
locs = []
if self.axes.yaxis._major_tick_kw["gridOn"]:
locs.extend(self.axes.yaxis.major.locator())
locs.extend(
self.axes.yaxis.major.locator._call_with_axis(self.axes.yaxis))
if self.axes.yaxis._minor_tick_kw["gridOn"]:
locs.extend(self.axes.yaxis.minor.locator())
locs.extend(
self.axes.yaxis.minor.locator._call_with_axis(self.axes.yaxis))
gridlines.extend([[x1, x2], [y, y]] for y in locs)

return gridlines
Expand Down
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