matplotlib · tacaswell · May 11, 2020 · Apr 29, 2020 · Apr 29, 2020 · Apr 29, 2020
diff --git a/doc/api/api_changes_3.3/behaviour.rst b/doc/api/api_changes_3.3/behaviour.rst
@@ -37,6 +37,13 @@ did nothing, when passed an unsupported value. It now raises a ``ValueError``.
 `.pyplot.tick_params`) used to accept any value for ``which`` and silently
 did nothing, when passed an unsupported value. It now raises a ``ValueError``.
 
+``Axis.set_ticklabels()`` must match ``FixedLocator.locs``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+If an axis is using a `.ticker.FixedLocator`, typically set by a call to
+`.Axis.set_ticks`, then the number of ticklabels supplied must match the
+number of locations available (``FixedFormattor.locs``).  If not, a
+``ValueError`` is raised.
+
 ``backend_pgf.LatexManager.latex``
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 ``backend_pgf.LatexManager.latex`` is now created with ``encoding="utf-8"``, so

diff --git a/examples/images_contours_and_fields/image_annotated_heatmap.py b/examples/images_contours_and_fields/image_annotated_heatmap.py
@@ -288,7 +288,7 @@ def annotate_heatmap(im, data=None, valfmt="{x:.2f}",
 # the diagonal elements (which are all 1) by using a
 # `matplotlib.ticker.FuncFormatter`.
 
-corr_matrix = np.corrcoef(np.random.rand(6, 5))
+corr_matrix = np.corrcoef(harvest)
 im, _ = heatmap(corr_matrix, vegetables, vegetables, ax=ax4,
                 cmap="PuOr", vmin=-1, vmax=1,
                 cbarlabel="correlation coeff.")

diff --git a/lib/matplotlib/axes/_base.py b/lib/matplotlib/axes/_base.py
@@ -3016,6 +3016,7 @@ def locator_params(self, axis='both', tight=None, **kwargs):
             self.yaxis.get_major_locator().set_params(**kwargs)
         self._request_autoscale_view(tight=tight,
                                      scalex=update_x, scaley=update_y)
+        self.stale = True
 
     def tick_params(self, axis='both', **kwargs):
         """

diff --git a/lib/matplotlib/axis.py b/lib/matplotlib/axis.py
@@ -3,6 +3,7 @@
 """
 
 import datetime
+import functools
 import logging
 
 import numpy as np
@@ -1599,6 +1600,11 @@ def set_pickradius(self, pickradius):
         """
         self.pickradius = pickradius
 
+    # Helper for set_ticklabels. Defining it here makes it pickleable.
+    @staticmethod
+    def _format_with_dict(tickd, x, pos):
+        return tickd.get(x, "")
+
     def set_ticklabels(self, ticklabels, *, minor=False, **kwargs):
         r"""
         Set the text values of the tick labels.
@@ -1626,14 +1632,34 @@ def set_ticklabels(self, ticklabels, *, minor=False, **kwargs):
         """
         ticklabels = [t.get_text() if hasattr(t, 'get_text') else t
                       for t in ticklabels]
+        locator = (self.get_minor_locator() if minor
+                   else self.get_major_locator())
+        if isinstance(locator, mticker.FixedLocator):
+            if len(locator.locs) != len(ticklabels):
+                raise ValueError(
+                    "The number of FixedLocator locations"
+                    f" ({len(locator.locs)}), usually from a call to"
+                    " set_ticks, does not match"
+                    f" the number of ticklabels ({len(ticklabels)}).")
+            tickd = {loc: lab for loc, lab in zip(locator.locs, ticklabels)}
+            func = functools.partial(self._format_with_dict, tickd)
+            formatter = mticker.FuncFormatter(func)
+        else:
+            formatter = mticker.FixedFormatter(ticklabels)
+
         if minor:
-            self.set_minor_formatter(mticker.FixedFormatter(ticklabels))
-            ticks = self.get_minor_ticks()
+            self.set_minor_formatter(formatter)
+            locs = self.get_minorticklocs()
+            ticks = self.get_minor_ticks(len(locs))
         else:
-            self.set_major_formatter(mticker.FixedFormatter(ticklabels))
-            ticks = self.get_major_ticks()
+            self.set_major_formatter(formatter)
+            locs = self.get_majorticklocs()
+            ticks = self.get_major_ticks(len(locs))
+
         ret = []
-        for tick_label, tick in zip(ticklabels, ticks):
+        for pos, (loc, tick) in enumerate(zip(locs, ticks)):
+            tick.update_position(loc)
+            tick_label = formatter(loc, pos)
             # deal with label1
             tick.label1.set_text(tick_label)
             tick.label1.update(kwargs)

diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -4441,8 +4441,8 @@ def test_set_get_ticklabels():
     # set ticklabel to 1 plot in normal way
     ax[0].set_xticks(range(10))
     ax[0].set_yticks(range(10))
-    ax[0].set_xticklabels(['a', 'b', 'c', 'd'])
-    ax[0].set_yticklabels(['11', '12', '13', '14'])
+    ax[0].set_xticklabels(['a', 'b', 'c', 'd'] + 6 * [''])
+    ax[0].set_yticklabels(['11', '12', '13', '14'] + 6 * [''])
 
     # set ticklabel to the other plot, expect the 2 plots have same label
     # setting pass get_ticklabels return value as ticklabels argument
@@ -4452,6 +4452,26 @@ def test_set_get_ticklabels():
     ax[1].set_yticklabels(ax[0].get_yticklabels())
 
 
+def test_subsampled_ticklabels():
+    # test issue 11937
+    fig, ax = plt.subplots()
+    ax.plot(np.arange(10))
+    ax.xaxis.set_ticks(np.arange(10) + 0.1)
+    ax.locator_params(nbins=5)
+    ax.xaxis.set_ticklabels([c for c in "bcdefghijk"])
-    ax.xaxis.set_ticks(np.arange(10) + 0.1)
-    ax.locator_params(nbins=5)
-    ax.xaxis.set_ticklabels([c for c in "bcdefghijk"])
+    ax.xaxis.set(ticks=np.arange(10) + 0.1),
+                 ticklabels=[c for c in "bcdefghijk"])
+    ax.locator_params(nbins=5)
-    ax.xaxis.set_ticks(np.arange(10) + 0.1)
-    ax.locator_params(nbins=5)
-    ax.xaxis.set_ticklabels([c for c in "bcdefghijk"])
+    ax.xaxis.set(ticks=np.arange(10) + 0.1),
+                 ticklabels=[c for c in "bcdefghijk"])
+    ax.locator_params(nbins=5)
+    plt.draw()
+    labels = [t.get_text() for t in ax.xaxis.get_ticklabels()]
+    assert labels == ['b', 'd', 'f', 'h', 'j']
+
+
+def test_mismatched_ticklabels():
+    fig, ax = plt.subplots()
+    ax.plot(np.arange(10))
+    ax.xaxis.set_ticks([1.5, 2.5])
+    with pytest.raises(ValueError):
+        ax.xaxis.set_ticklabels(['a', 'b', 'c'])
+
+
 @image_comparison(['retain_tick_visibility.png'])
 def test_retain_tick_visibility():
     fig, ax = plt.subplots()

diff --git a/lib/matplotlib/ticker.py b/lib/matplotlib/ticker.py
@@ -381,8 +381,10 @@ class FuncFormatter(Formatter):
     position ``pos``), and return a string containing the corresponding
     tick label.
     """
+
     def __init__(self, func):
         self.func = func
+        self.offset_string = ""
 
     def __call__(self, x, pos=None):
         """
@@ -392,6 +394,12 @@ def __call__(self, x, pos=None):
         """
         return self.func(x, pos)
 
+    def get_offset(self):
+        return self.offset_string
+
+    def set_offset_string(self, ofs):
+        self.offset_string = ofs
+
 
 class FormatStrFormatter(Formatter):
     """