[Python-Dev] Making None a keyword (original) (raw)

Guido van Rossum guido@python.org
Fri, 26 Apr 2002 08:10:24 -0400

> I'd like to make None a keyword. This prevents dumb users from > assigning to it and screwing themselves, and can cause a slight > speedup because using None avoids two dict lookups. > > - Any objections?

+1 but only if you use the standard mechanism for this: warnings in 2.3, SyntaxError in 2.4.

Good point.

> - Can somebody help me implement this? I've got the parser changes > ready, but not the compiler changes. > > Believe it or not, Zope3 contains code that will break with this > change: there are functions with a default argument of the form > None=None as a speedup hack. I think this is an argument for the > change. :-)

Zope3 is not the only software using these kind of hacks to work around the builtins lookups.

I just realized there's another use for None as an identifier that is currently totally legal and which would become illegal: it's conceivable that someone would use None as an attribute name, e.g.

class C:
    def None(self): pass

C().None()

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