Positional-only parameters for Python [LWN.net]

Positional-only parameters for Python

Posted Apr 10, 2019 20:52 UTC (Wed) by yootis (subscriber, #4762)
Parent article: Positional-only parameters for Python

Why is it ever actually necessary to prevent the use of keyword arguments? The article mentions "what if the API changes", but to me that's all the more reason to use keyword arguments. At least you'd detect the problem. Forcing positional arguments sounds dangerous to me.

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Positional-only parameters for Python

Posted Apr 10, 2019 22:08 UTC (Wed) by quotemstr (subscriber, #45331) [Link] (1 responses)

One problem is API signature ambiguity. Say I have a def foo(bar): return bar +1. People right now are allowed to call foo as foo(5) or foo(bar=5). Now suppose I want to refactor foo as "def foo(qux):return 1+qux". Is the change of the argument name a breaking API change? Only if w allow keyword argument specification for bar! Right now, we have to treat argument names as part of a function's signature, and I think that's too constricting.

Positional-only parameters for Python

Posted Apr 11, 2019 2:11 UTC (Thu) by k8to (guest, #15413) [Link]

It seems valuable to have a choice on whether to expose the names or not. However, there are many modules where the docs don't talk about the argument names, but keyword arguments make the consuming code vastly more readable.

I think the fact that the arg names are exposed by default is essentially a good accident that forces interfaces to be a bit more usable than they are by default.

Amusingly I went to a good deal of trouble in some code I made to make the args keyword-only without making the implementation of the callsites harder to read. I had explicit documentation of how calls were required to be made, but used inspection to enforce it. I could used def func(**kwargs) but manually coding all the dispatch would have been really unfortunate.