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Wed Oct 9 22:51:30 CEST 2013 · https://mail.python.org/pipermail/python-dev/2013-October/129347.html

On 10/09/2013 10:46 PM, 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
>     ...

That's a clever, and intuitive, idea.  Though the try/excepts look 
awfully clumsy.

Perhaps we could add (egad, no, I can't believe I'm saying this) a new 
built-in function that tells you whether or not a local variable has 
been assigned to yet?

    def range([start,] stop, [step], /):
         if not bound(start):
             start = 0
         if not bound(step):
             step = 1
         ...

Anyway, this section is in the "Notes For Future Implementors" section, 
so as long as we never actually implement the syntax we don't need to 
solve the problem.

//arry/
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Showing content from https://mail.python.org/pipermail/python-dev/2013-October/129347.html below:

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