[Python-ideas] [Python-Dev] nodef

[Martin Blais]

On 5/23/07, Collin Winter <collinw at gmail.com> wrote:
> [moving to python-ideas, where it belongs]
>
> > I think Python needs a builtin for this very purpose.  I propose
> > 'nodef', a unique object whose sole purpose is to serve as a default
> > value.  It should be unique, in the same sense that 'None' is unique.
>
> I've run into this situation several times before, and I've never felt
> that defining my own sentinel was unduly taxing. Having a built-in
> would only save a single line, the initial "sentinel = object()".

There is another benefit to a builtin 'nodef', BTW, which is that of a
consistent meaning for the word.  Having a consistent name for this
concept--across all programs, if it were in the language--makes it
more obvious what you're trying to achieve.  Otherwise, you decide to
use 'sentinel', I choose 'NoDef', Barry uses 'missing', and we're all
speaking a different "language".

Thought I do admit that the possibility of misuse of a builtin 'nodef'
is slightly troubling.  I guess object() is our (gensym), I did not
know that.

cheers,