[Python-Dev] PEP 457: Syntax For Positional-Only Parameters (original) (raw)

Larry Hastings larry at hastings.org
Wed Oct 9 22:51:30 CEST 2013

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.

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