Transform ParasiteAxesBase._update_viewlim into standard callback.

update_viewlim as an independent method was deprecated in da2f77a and
has since then been removed.  We could just inline _update_viewlim into
apply_aspect, but transforming it into a callback on
xlim_changed/ylim_changed helps moving towards the removal of
ParasiteAxes as a separate class and its replacement by standard (child)
axes with some extra attributes/callbacks set.

Author: anntzer

doc/api/prev_api_changes/api_changes_3.6.0/removals.rst

@@ -152,7 +152,7 @@ The following class methods have been removed:
   ``RendererAgg.tostring_rgba_minimized()``
 - ``NavigationToolbar2Wx.get_canvas()``
 
-- ``ParasiteAxesBase.update_viewlim()``; use `.ParasiteAxesBase.apply_aspect`
+- ``ParasiteAxesBase.update_viewlim()``; use ``ParasiteAxesBase.apply_aspect``
   instead.
 - ``Subplot.get_geometry()``; use ``SubplotBase.get_subplotspec`` instead.
 - ``Subplot.change_geometry()``; use ``SubplotBase.set_subplotspec`` instead.

lib/mpl_toolkits/axes_grid1/parasite_axes.py

@@ -19,6 +19,10 @@ def clear(self):
         super().clear()
         martist.setp(self.get_children(), visible=False)
         self._get_lines = self._parent_axes._get_lines
+        self._parent_axes.callbacks._connect_picklable(
+            "xlim_changed", self._sync_lims)
+        self._parent_axes.callbacks._connect_picklable(
+            "ylim_changed", self._sync_lims)
 
     def pick(self, mouseevent):
         # This most likely goes to Artist.pick (depending on axes_class given
@@ -52,23 +56,18 @@ def set_viewlim_mode(self, mode):
     def get_viewlim_mode(self):
         return self._viewlim_mode
 
-    def _update_viewlim(self):  # Inline after deprecation elapses.
-        viewlim = self._parent_axes.viewLim.frozen()
+    def _sync_lims(self, parent):
+        viewlim = parent.viewLim.frozen()
         mode = self.get_viewlim_mode()
         if mode is None:
             pass
         elif mode == "equal":
-            self.axes.viewLim.set(viewlim)
+            self.viewLim.set(viewlim)
         elif mode == "transform":
-            self.axes.viewLim.set(
-                viewlim.transformed(self.transAux.inverted()))
+            self.viewLim.set(viewlim.transformed(self.transAux.inverted()))
         else:
             _api.check_in_list([None, "equal", "transform"], mode=mode)
 
-    def apply_aspect(self, position=None):
-        self._update_viewlim()
-        super().apply_aspect()
-
     # end of aux_transform support
 
 
@@ -140,9 +139,9 @@ def draw(self, renderer):
         self._children = self._children[:orig_children_len]
 
     def clear(self):
+        super().clear()
         for ax in self.parasites:
             ax.clear()
-        super().clear()
 
     def pick(self, mouseevent):
         super().pick(mouseevent)