On 4/27/07, Thomas Lotze <[EMAIL PROTECTED]> wrote: > Guido van Rossum wrote: > > > Another constraint is that hashable objects, once created, should > > never change their value (as compared by ``==``) or their hash value. > > If a class cannot guarantee this, it should not derive from > > ``Hashable``; if it cannot guarantee this for certain instances only, > > ``__hash__`` for those instances should raise a ``TypeError`` > > exception. > > Shouldn't this rather be a ValueError since it occurs not because of the > type of the object in question, but its value (while in general, there are > instances of the same type representing other values which are hashable)?
>>> hash([]) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: list objects are unhashable Normally the exception is raised because the type is wrong. Requiring both TypeError and ValueError be caught just for this special case would be confusing. A subclass of both could be created, but that seems pedantic with no practical value. -- Adam Olsen, aka Rhamphoryncus _______________________________________________ Python-3000 mailing list Python-3000@python.org http://mail.python.org/mailman/listinfo/python-3000 Unsubscribe: http://mail.python.org/mailman/options/python-3000/archive%40mail-archive.com
