No need to return OrderedDict from _gen_axes_spines.

There's already some subclasses that return a plain dict (e.g., geo
axes); moreover, the return value is passed to Spine.from_dict which
anyways `**kwargs`-expands it, so that stage also affects whether order
is maintained.

Author: anntzer

lib/matplotlib/axes/_base.py

@@ -1,4 +1,3 @@
-from collections import OrderedDict
 from collections.abc import MutableSequence
 from contextlib import ExitStack
 import functools
@@ -1160,8 +1159,8 @@ def _gen_axes_spines(self, locations=None, offset=0.0, units='inches'):
         -----
         Intended to be overridden by new projection types.
         """
-        return OrderedDict((side, mspines.Spine.linear_spine(self, side))
-                           for side in ['left', 'right', 'bottom', 'top'])
+        return {side: mspines.Spine.linear_spine(self, side)
+                for side in ['left', 'right', 'bottom', 'top']}
 
     def sharex(self, other):
         """

lib/matplotlib/projections/polar.py

@@ -1,4 +1,3 @@
-from collections import OrderedDict
 import math
 import types
 
@@ -12,7 +11,7 @@
 from matplotlib.path import Path
 import matplotlib.ticker as mticker
 import matplotlib.transforms as mtransforms
-import matplotlib.spines as mspines
+from matplotlib.spines import Spine
 
 
 class PolarTransform(mtransforms.Transform):
@@ -964,14 +963,12 @@ def _gen_axes_patch(self):
         return mpatches.Wedge((0.5, 0.5), 0.5, 0.0, 360.0)
 
     def _gen_axes_spines(self):
-        spines = OrderedDict([
-            ('polar', mspines.Spine.arc_spine(self, 'top',
-                                              (0.5, 0.5), 0.5, 0.0, 360.0)),
-            ('start', mspines.Spine.linear_spine(self, 'left')),
-            ('end', mspines.Spine.linear_spine(self, 'right')),
-            ('inner', mspines.Spine.arc_spine(self, 'bottom',
-                                              (0.5, 0.5), 0.0, 0.0, 360.0))
-        ])
+        spines = {
+            'polar': Spine.arc_spine(self, 'top', (0.5, 0.5), 0.5, 0, 360),
+            'start': Spine.linear_spine(self, 'left'),
+            'end': Spine.linear_spine(self, 'right'),
+            'inner': Spine.arc_spine(self, 'bottom', (0.5, 0.5), 0.0, 0, 360),
+        }
         spines['polar'].set_transform(self.transWedge + self.transAxes)
         spines['inner'].set_transform(self.transWedge + self.transAxes)
         spines['start'].set_transform(self._yaxis_transform)