[Python-Dev] python 3 niggle: None < 1 raises TypeError

[Terry Reedy]

On 2/17/2014 5:25 PM, Nick Coghlan wrote:
>
> On 17 Feb 2014 22:25, "M.-A. Lemburg" <mal at egenix.com
> <mailto:mal at egenix.com>> wrote:

>  > default_3way_compare(PyObject *v, PyObject *w)
>  > ...
>  >     /* None is smaller than anything */

Unless it is not, as with datetimes, perhaps other classes written 
similarly, and some user class instances.

>  > Note that it's not important whether None is smaller or greater
>  > than any other object. The important aspect is that it's sorting
>  > order is consistent and doesn't raise a TypeError when doing an
>  > ordered comparison with other objects.
>
> Thanks, that's enough to persuade me that it is a good idea to restore
> that behaviour

Would you restore the actual sometimes inconsistent 2.x behavior or 
implement something new -- what M-A claims but never was? I doubt the 
former would be trivial since it was part of the now deleted cmp and 
3way machinery. To make None a true bottom object, the rich comparison 
methods would have to special-case None as either argument before 
looking at the __rc__ special methods of either.

Regardless of how implemented, such a change would break user code that 
defines a Bottom class and depends on Bottom() < None == True. Given the 
python-ideas discussions about adding a top or bottom class, I expect 
that such classes are in use. So a deprecation period would be needed, 
pushing the change off to 3.7. It is also possible that someone took the 
ending of cross-type comparisons seriously and is depending on the 
TypeError.

while True:
   x = f(args)
   try:
     if x > 10: a(x)
     else: b(x)
   except TypeError:
     # f did not return a number
     break

-- 
Terry Jan Reedy