axes_grid1: make twin* not modify host axes

smheidrich · smheidrich · commit e499b2fed102 · 2019-01-04T00:51:53.000+01:00
PR #4898 changed the behavior of twinx() and twiny() in axes_grid1 to make them consistent with twin(). This commit inverts the "direction" of consistency and makes twin() behave like the pre-#4898 twinx() and twiny() instead. This way, the API becomes less surprising: instead of hiding certain host axes, twin* now keeps the host axes unmodified, while the parasite axes have their axis lines hidden instead. Unfortunately, this change breaks backwards-compatibility for code relying on the specifics of host and parasite axes visibility. Helps with #10748.
diff --git a/doc/api/next_api_changes/2019-01-04-SH.rst b/doc/api/next_api_changes/2019-01-04-SH.rst
@@ -0,0 +1,11 @@
+Changes to ``twin*`` methods in `~.mpl_toolkits.axes_grid1`
+-----------------------------------------------------------
+
+Previously, calling ``twin``, ``twinx`` and ``twiny`` on
+`~.mpl_toolkits.axes_grid1` host axes would hide the host axes' own axis lines
+so that there is no overdrawing with the twin/parasite axes' axis lines. This
+could lead to surprising behavior in certain cases
+([#10748](https://github.com/matplotlib/matplotlib/issues/10748)), so the
+logic has now been reversed. I.e., host axis lines are kept and twin/parasite
+axis lines hidden. This may break code which relies on the specifics of
+host/parasite axis line visibility.
diff --git a/lib/mpl_toolkits/axes_grid1/parasite_axes.py b/lib/mpl_toolkits/axes_grid1/parasite_axes.py
@@ -249,17 +249,15 @@ def twinx(self, axes_class=None):
         self.parasites.append(ax2)
         ax2._remove_method = self._remove_twinx
 
-        self.axis["right"].set_visible(False)
-
         ax2.axis["right"].set_visible(True)
+        ax2.axis["right"].toggle(all=True)
+        ax2.axis["right"].line.set_visible(False)
         ax2.axis["left", "top", "bottom"].set_visible(False)
 
         return ax2
 
     def _remove_twinx(self, ax):
         self.parasites.remove(ax)
-        self.axis["right"].set_visible(True)
-        self.axis["right"].toggle(ticklabels=False, label=False)
 
     def twiny(self, axes_class=None):
         """
@@ -278,17 +276,15 @@ def twiny(self, axes_class=None):
         self.parasites.append(ax2)
         ax2._remove_method = self._remove_twiny
 
-        self.axis["top"].set_visible(False)
-
         ax2.axis["top"].set_visible(True)
+        ax2.axis["top"].toggle(all=True)
+        ax2.axis["top"].line.set_visible(False)
         ax2.axis["left", "right", "bottom"].set_visible(False)
 
         return ax2
 
     def _remove_twiny(self, ax):
         self.parasites.remove(ax)
-        self.axis["top"].set_visible(True)
-        self.axis["top"].toggle(ticklabels=False, label=False)
 
     def twin(self, aux_trans=None, axes_class=None):
         """
@@ -313,15 +309,13 @@ def twin(self, aux_trans=None, axes_class=None):
         self.parasites.append(ax2)
         ax2._remove_method = self.parasites.remove
 
-        self.axis["top", "right"].set_visible(False)
-
         ax2.axis["top", "right"].set_visible(True)
+        ax2.axis["top", "right"].toggle(all=True)
+        ax2.axis["top", "right"].line.set_visible(False)
         ax2.axis["left", "bottom"].set_visible(False)
 
         def _remove_method(h):
             self.parasites.remove(h)
-            self.axis["top", "right"].set_visible(True)
-            self.axis["top", "right"].toggle(ticklabels=False, label=False)
         ax2._remove_method = _remove_method
 
         return ax2
diff --git a/lib/mpl_toolkits/tests/baseline_images/test_axes_grid1/twin_axes_empty_and_removed.png b/lib/mpl_toolkits/tests/baseline_images/test_axes_grid1/twin_axes_empty_and_removed.png
