[Python-Dev] PEP 457: Syntax For Positional-Only Parameters

[Steven D'Aprano]

On Wed, Oct 09, 2013 at 09:46:00PM +0100, Mark Shannon wrote:

> There is no need to create an "undefined" value.
> Rather than define a parameter by assigning a fake value, just don't 
> define it. We already do this for non-parameter locals and it could be 
> extended to parameters.
> 
> 'range' would be defined thus:
> 
> def range([start,] stop, [step], /):
>     try:
>         start
>     except UnboundLocalError:
>         start = 0
>     try:
>         step
>     except UnboundLocalError:
>         step = 1
>     ...


If there is even the tiniest, faintest chance that positional arguments 
will be available to functions written in Python some day, -1 to this 
suggestion. There is no way I want to write code like the above instead 
of:

def range([start,] stop, [step,] /):
    if start is Undefined:
        start = 0
    if step is Undefined:
        step = 1


But what I really want to write is this:

def range(start=0, stop, step=1, /):
    ...


although maybe we don't want to encourage odd calling signatures by 
making them too easy to write.


-- 
Steven