Merge pull request matplotlib#1169 from leejjoon/fix-subplot-twinxy

Subplot.twin[xy] returns a Subplot instance

Author: efiring

doc/api/api_changes.rst

@@ -120,6 +120,10 @@ Changes in 1.2.x
   ``ax.transData + ax.transAxes.inverted()`` (depth is a new concept, but had it existed 
   it would return 4 for this example).      
 
+* ``twinx`` and ``twiny`` now returns an instance of SubplotBase if
+  parent axes is an instance of SubplotBase.
+  
+
 Changes in 1.1.x
 ================
 

lib/matplotlib/axes.py

@@ -7677,6 +7677,14 @@ def table(self, **kwargs):
         """
         return mtable.table(self, **kwargs)
 
+    def _make_twin_axes(self, *kl, **kwargs):
+        """
+        make a twinx axes of self. This is used for twinx and twiny.
+        """
+        ax2 = self.figure.add_axes(self.get_position(True), *kl, **kwargs)
+        return ax2
+
+
     def twinx(self):
         """
         Call signature::
@@ -7693,8 +7701,7 @@ def twinx(self):
             events are only called for the artists in the top-most axes.
         """
 
-        ax2 = self.figure.add_axes(self.get_position(True), sharex=self,
-            frameon=False)
+        ax2 = self._make_twin_axes(sharex=self, frameon=False)
         ax2.yaxis.tick_right()
         ax2.yaxis.set_label_position('right')
         ax2.yaxis.set_offset_position('right')
@@ -7718,8 +7725,7 @@ def twiny(self):
             events are only called for the artists in the top-most axes.
         """
 
-        ax2 = self.figure.add_axes(self.get_position(True), sharey=self,
-            frameon=False)
+        ax2 = self._make_twin_axes(sharey=self, frameon=False)
         ax2.xaxis.tick_top()
         ax2.xaxis.set_label_position('top')
         self.xaxis.tick_bottom()
@@ -8899,6 +8905,13 @@ def label_outer(self):
             label.set_visible(firstcol)
 
 
+    def _make_twin_axes(self, *kl, **kwargs):
+        """
+        make a twinx axes of self. This is used for twinx and twiny.
+        """
+        ax2 = self.figure.add_subplot(self.get_subplotspec(), *kl, **kwargs)
+        return ax2
+
 
 _subplot_classes = {}
 def subplot_class_factory(axes_class=None):