If the built-in hash function returned -1 when a custom __hash__ method did so, then custom numeric classes following the hashing guidelines in the Python Langu

If the built-in hash function returned -1 when a custom __hash__ method did so, then custom numeric classes following the hashing guidelines in the Python Language Reference designed to maintain the x==y => hash(x)==hash(y) invariant would fail to maintain that invariant on the reference implementation of Python due to a CPython implementation detail, which would be a Bad Thing™.