Add _can_unconvert_units property

dstansby · dstansby · commit 01ecacaa1252 · 2019-05-24T16:54:55.000+02:00
diff --git a/lib/matplotlib/axes/_base.py b/lib/matplotlib/axes/_base.py
@@ -3176,7 +3176,7 @@ def _convert_back_lim(self, lim, axis):
         """
         Helper method to convert axis limits back to unitized data.
         """
-        if axis.converter is not None:
+        if axis._can_unconvert_units:
             lim = [axis.converter.un_convert(l, axis.units, axis) for
                    l in lim]
         return tuple(lim)
diff --git a/lib/matplotlib/axis.py b/lib/matplotlib/axis.py
@@ -1581,8 +1581,15 @@ def convert_units(self, x):
                                          f'units: {x!r}') from e
         return ret
 
+    @property
+    def _can_unconvert_units(self):
+        if self.converter is not None:
+            if hasattr(self.converter, 'un_convert'):
+                return True
+        return False
+
     def unconvert_units(self, x):
-        if self.converter is None:
+        if not self._can_unconvert_units:
             return x
         return self.converter.un_convert(x, self.units, self)
 
