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

Larry Hastings larry at hastings.org
Wed Oct 9 16:15:36 CEST 2013

On 10/09/2013 11:46 AM, Nick Coghlan wrote:

Generally, it needs to be a bit clearer that the intent of the PEP isn't to say "let's do this", it's to be explicit that acceptance of the Argument Clinic PEP severely constrains the design space for possible solutions if we ever did implement Python level support for positional only arguments.

Can you suggest an edit that would make you happy?

- parameters in optional groups should just have an implied "=None" that can be overriden if desired.

No no no! You can't have a default value, and you definitely couldn't use None.

range() decides what its arguments mean based on how many arguments it receives. If I understand your proposal correctly, you suggest that

range(None, 5)

would return the same result as

range(5)

But that's simply not how it works.

If you want to propose changing the semantics of range, go ahead, I'll stand back.

- a simpler variant that omits the grouping support and only allows optional parameters on the right should also be reserved

If that syntax is a subset of this syntax, and this syntax is reserved, then by extension we would automatically reserve that syntax too. In any other circumstance (this PEP is rejected, the simpler variant uses a different syntax) the simpler syntax should get a new PEP.

I'll just say that that syntax is insufficient to implement existing functions we all know and love (addch, range).

- explicitly delegate to the argument clinic PEP for the impact on inspect.Signature

I'd actually rather do it the other way 'round. This PEP is a better place for it. Even though I think the Clinic PEP has a higher chance of being accepted ;-)

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