Second attempt at fixing axis inversion (for mpl3.1).

anntzer · anntzer · commit 7f7b04879c71 · 2019-06-28T10:00:43.000+02:00
Turns out that the behavior of nonsingular() and limit_range_for_scale()
w.r.t. respecting argument order is all over the place, so just re-sort
the axis limits after-the-fact.
diff --git a/lib/matplotlib/axes/_base.py b/lib/matplotlib/axes/_base.py
@@ -3264,11 +3264,10 @@ def set_xlim(self, left=None, right=None, emit=True, auto=False,
             cbook._warn_external(
                 f"Attempting to set identical left == right == {left} results "
                 f"in singular transformations; automatically expanding.")
-        swapped = left > right
+        reverse = left > right
         left, right = self.xaxis.get_major_locator().nonsingular(left, right)
         left, right = self.xaxis.limit_range_for_scale(left, right)
-        if swapped:
-            left, right = right, left
+        left, right = sorted([left, right], reverse=reverse)
 
         self.viewLim.intervalx = (left, right)
         if auto is not None:
@@ -3647,11 +3646,10 @@ def set_ylim(self, bottom=None, top=None, emit=True, auto=False,
                 f"Attempting to set identical bottom == top == {bottom} "
                 f"results in singular transformations; automatically "
                 f"expanding.")
-        swapped = bottom > top
+        reverse = bottom > top
         bottom, top = self.yaxis.get_major_locator().nonsingular(bottom, top)
         bottom, top = self.yaxis.limit_range_for_scale(bottom, top)
-        if swapped:
-            bottom, top = top, bottom
+        bottom, top = sorted([bottom, top], reverse=reverse)
 
         self.viewLim.intervaly = (bottom, top)
         if auto is not None:
diff --git a/lib/mpl_toolkits/mplot3d/axes3d.py b/lib/mpl_toolkits/mplot3d/axes3d.py
@@ -623,11 +623,10 @@ def set_xlim3d(self, left=None, right=None, emit=True, auto=False,
             cbook._warn_external(
                 f"Attempting to set identical left == right == {left} results "
                 f"in singular transformations; automatically expanding.")
-        swapped = left > right
+        reverse = left > right
         left, right = self.xaxis.get_major_locator().nonsingular(left, right)
         left, right = self.xaxis.limit_range_for_scale(left, right)
-        if swapped:
-            left, right = right, left
+        left, right = sorted([left, right], reverse=reverse)
         self.xy_viewLim.intervalx = (left, right)
 
         if auto is not None:
