Forward port only Py3k relevant change in r65642 (giving it a Py3k NEWS entry anyway because of the difference in the changes between the two branches)

Lib/numbers.py

@@ -15,6 +15,8 @@ class Number(metaclass=ABCMeta):
     If you just want to check if an argument x is a number, without
     caring what kind, use isinstance(x, Number).
     """
+    # Concrete numeric types must provide their own hash implementation
+    __hash__ = None
 
 
 ## Notes on Decimal

Misc/NEWS

@@ -30,6 +30,12 @@ Core and Builtins
 Library
 -------
 
+- Issue #2235: numbers.Number now blocks inheritance of the default id()
+  based hash because that hash mechanism is not correct for numeric types.
+  All concrete numeric types that inherit from Number (rather than just
+  registering with it) must explicitly provide a hash implementation in
+  order for their instances to be hashable.
+
 - Issue #2676: in the email package, content-type parsing was hanging on
   pathological input because of quadratic or exponential behaviour of a
   regular expression.