Fix broken example, add to api_changes, tweak error message.

efiring · efiring · commit 629143041791 · 2020-05-04T13:05:03.000-10:00
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 `.tickers.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
@@ -289,7 +289,7 @@ def annotate_heatmap(im, data=None, valfmt="{x:.2f}",
 # `matplotlib.ticker.FuncFormatter`.
 
 corr_matrix = np.corrcoef(np.random.rand(6, 5))
-im, _ = heatmap(corr_matrix, vegetables, vegetables, ax=ax4,
+im, _ = heatmap(corr_matrix, vegetables, farmers, ax=ax4,
                 cmap="PuOr", vmin=-1, vmax=1,
                 cbarlabel="correlation coeff.")
 
diff --git a/lib/matplotlib/axis.py b/lib/matplotlib/axis.py
@@ -1638,7 +1638,8 @@ def set_ticklabels(self, ticklabels, *, minor=False, **kwargs):
             if len(locator.locs) != len(ticklabels):
                 raise ValueError(
                     "The number of FixedLocator locations"
-                    f" ({len(locator.locs)}) does not match"
+                    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)
