unchain exception

Author: ethanfurman

Lib/enum.py

@@ -207,7 +207,7 @@ def __get__(self, instance, ownerclass=None):
                 except KeyError:
                     raise AttributeError(
                             '%r has no attribute %r' % (ownerclass, self.name)
-                            )
+                            ) from None
             else:
                 return self.fget(instance)