[Python-Dev] Making None a keyword

[Guido van Rossum]

> [Guido]
> > ...
> > It needs to add 'None' as an alternative to all other places where
> > currently NAME occurs.
> 
> Fudge.  None makes no sense anywhere in, e.g.,
> 
> dotted_name: NAME ('.' NAME)*
> 
> or
> 
>     global_stmt: 'global' NAME (',' NAME)*
> 
> but I suppose it has to be allowed for in 2.3 anyway else an existing

Yes, that's (alas) the point.

>     import None.None.None as None
> 
> would yield a SyntaxError instead of a warning.

More realistically,

    def foo(a, None=None):
        if a is None: ...

I found 4 examples of this in Zope3 alone, and MAL has some too.

> Note too that we can't change the generated code at all for 2.3
> unless under the control of a new future statement, else existing
> None-abusing code could break.

A future statement makes no sense for this, so I guess all we can do
in 2.3 is warn about use of None in all contexts except in
expressions.

This is really too bad -- I wish we could decide to just break code
(since it's a clean break) but apparently that's unacceptable to the
users.

--Guido van Rossum (home page: http://www.python.org/~guido/)