Document that axes unsharing is impossible.

The feature may perhaps be desirable, but let's document the current
state of things.

Author: anntzer

lib/matplotlib/axes/_base.py

@@ -597,7 +597,8 @@ def __init__(self, fig,
 
         sharex, sharey : `~matplotlib.axes.Axes`, optional
             The x- or y-`~.matplotlib.axis` is shared with the x- or y-axis in
-            the input `~.axes.Axes`.
+            the input `~.axes.Axes`.  Note that it is not possible to unshare
+            axes.
 
         frameon : bool, default: True
             Whether the Axes frame is visible.
@@ -1221,7 +1222,7 @@ def sharex(self, other):
 
         This is equivalent to passing ``sharex=other`` when constructing the
         Axes, and cannot be used if the x-axis is already being shared with
-        another Axes.
+        another Axes.  Note that it is not possible to unshare axes.
         """
         _api.check_isinstance(_AxesBase, other=other)
         if self._sharex is not None and other is not self._sharex:
@@ -1240,7 +1241,7 @@ def sharey(self, other):
 
         This is equivalent to passing ``sharey=other`` when constructing the
         Axes, and cannot be used if the y-axis is already being shared with
-        another Axes.
+        another Axes.  Note that it is not possible to unshare axes.
         """
         _api.check_isinstance(_AxesBase, other=other)
         if self._sharey is not None and other is not self._sharey:

lib/matplotlib/figure.py

@@ -755,6 +755,8 @@ def subplots(self, nrows=1, ncols=1, *, sharex=False, sharey=False,
             When subplots have a shared axis that has units, calling
             `.Axis.set_units` will update each axis with the new units.
 
+            Note that it is not possible to unshare axes.
+
         squeeze : bool, default: True
             - If True, extra dimensions are squeezed out from the returned
               array of Axes:

lib/matplotlib/pyplot.py

@@ -1651,8 +1651,9 @@ def subplots(
         on, use `~matplotlib.axes.Axes.tick_params`.
 
         When subplots have a shared axis that has units, calling
-        `~matplotlib.axis.Axis.set_units` will update each axis with the
-        new units.
+        `.Axis.set_units` will update each axis with the new units.
+
+        Note that it is not possible to unshare axes.
 
     squeeze : bool, default: True
         - If True, extra dimensions are squeezed out from the returned

lib/mpl_toolkits/mplot3d/axes3d.py

@@ -84,7 +84,8 @@ def __init__(
             axis. A positive angle spins the camera clockwise, causing the
             scene to rotate counter-clockwise.
         sharez : Axes3D, optional
-            Other Axes to share z-limits with.
+            Other Axes to share z-limits with.  Note that it is not possible to
+            unshare axes.
         proj_type : {'persp', 'ortho'}
             The projection type, default 'persp'.
         box_aspect : 3-tuple of floats, default: None
@@ -108,7 +109,8 @@ def __init__(
             The focal length can be computed from a desired Field Of View via
             the equation: focal_length = 1/tan(FOV/2)
         shareview : Axes3D, optional
-            Other Axes to share view angles with.
+            Other Axes to share view angles with.  Note that it is not possible
+            to unshare axes.
 
         **kwargs
             Other optional keyword arguments:
@@ -1308,7 +1310,7 @@ def sharez(self, other):
 
         This is equivalent to passing ``sharez=other`` when constructing the
         Axes, and cannot be used if the z-axis is already being shared with
-        another Axes.
+        another Axes.  Note that it is not possible to unshare axes.
         """
         _api.check_isinstance(Axes3D, other=other)
         if self._sharez is not None and other is not self._sharez:
@@ -1325,9 +1327,9 @@ def shareview(self, other):
         """
         Share the view angles with *other*.
 
-        This is equivalent to passing ``shareview=other`` when
-        constructing the Axes, and cannot be used if the view angles are
-        already being shared with another Axes.
+        This is equivalent to passing ``shareview=other`` when constructing the
+        Axes, and cannot be used if the view angles are already being shared
+        with another Axes.  Note that it is not possible to unshare axes.
         """
         _api.check_isinstance(Axes3D, other=other)
         if self._shareview is not None and other is not self._shareview: