Support alias inheritance.

anntzer · anntzer · commit 2d66f0f170cc · 2018-01-01T20:18:59.000-08:00
diff --git a/lib/matplotlib/cbook/__init__.py b/lib/matplotlib/cbook/__init__.py
@@ -11,6 +11,7 @@
 import six
 from six.moves import xrange, zip
 import collections
+import copy
 import datetime
 import errno
 import functools
@@ -2783,7 +2784,8 @@ class so far, an alias named ``get_alias`` will be defined; the same will
     exception will be raised.
 
     The alias map is stored as the ``_alias_map`` attribute on the class and
-    can be used by `~.normalize_kwargs`.
+    can be used by `~.normalize_kwargs` (which assumes that higher priority
+    aliases come last).
     """
     if cls is None:
         return functools.partial(_define_aliases, alias_d)
@@ -2804,7 +2806,15 @@ def method(self, *args, **kwargs):
                     method.__doc__ = "alias for `{}`".format(prefix + prop)
                     setattr(cls, prefix + alias, method)
         if not exists:
-            raise ValueError("property {} does not exist".format(prop))
+            raise ValueError(
+                "Neither getter nor setter exists for {!r}".format(prop))
 
-    cls._alias_map = alias_d
+    try:
+        # Deepcopy the inherited alias map if any, to avoid modifying the
+        # parent class.
+        cls._alias_map = copy.deepcopy(cls._alias_map)
+    except AttributeError:
+        cls._alias_map = {}
+    for prop, aliases in alias_d.items():
+        cls._alias_map.setdefault(prop, []).extend(aliases)
     return cls
