Has anyone done a survey of, say, the cpython library codebase to see what
proportion of arguments lists would significantly benefit from this PEP
given as a proportion of the total codebase? In all the Python I've ever
written or seen, I can only thing of one example of a custom sentinel ever
being needed.
I think people are significantly underestimating the cognitive load this
feature would add.
On Saturday, December 4, 2021 at 11:01:44 PM UTC-5 David Mertz, Ph.D. wrote:
> On Sat, Dec 4, 2021, 10:14 PM Rob Cliffe via Python-ideas
>
>> The designers of 12 languages have chosen to provide late binding; those
>> of 3 or 4 have provided early binding.
>> I think this is at least tenuous evidence in favour of my belief that
>> late binding is more useful than early binding.
>>
>
> As the person probably most vociferous in opposing this PEP,
>
I absolutely agree that late-binding is more useful. If I were creating a
> new programming language today, I would certainly make arguments be
> evaluated on call, not on definition.
>
> There are perfectly good ways to "fake" either one if you only have the
> other. Probably more work is needed to simulate early binding, but there
> are ways to achieve the same effect.
>
> However, that language would not be Python. That ship sailed in 1991.
> What's being discussed here isn't changing the behavior of binding in `def
> f(foo=bar)`.
>
> Instead, it's a discussion of adding ADDITIONAL syntax for late-binding
> behavior. I think the proposed syntax is the worst of all the options
> discussed. But the real issue is that the cases where it is relevant are
> vanishingly rate, and the extra cognitive, teaching, and maintenance burden
> is significant.
>
> In 90%+ of the functions I've written, default arguments are non-sentinel
> immutable values. If those were late bound, nothing whatsoever would
> change. Yes, maybe slightly different bytecodes would exist, but at the
> Python level, everything works work the same.
>
> So this issue only issue is only remotely relevant to <10% of functions
> with default arguments. However, of those <10%, 98% work perfectly fine
> with None as a sentinel.
>
> Probably fewer than half of functions I've written use named parameters at
> all.
>
> In other words, for somewhere fewer than one in a thousand functions, this
> new syntax might serve any purpose at all. That purpose is predominantly
> "avoid using a custom sentinel." A custom sentinel is a SMALL lift. I agree
> that a custom sentinel, while rare, is a slight wart in a program.
>
> I also believe that in this 1/1000 case, there could be a slightly
> prettier automatic docstrings. But not prettier than writing an explicit
> docstring in any case.
>
> The cost here is that EVERY SINGLE student learning Python needs to add
> this new construct to their mental load. EVERY book and tutorial needs to
> be updated. EVERY experienced developer has to spend extra effort
> understanding and writing code.
>
> The COST of implementing this PEP is *quite literally* tens of millions of
> person days. The benefit is a rare savings of two lines of function body
> code or a docstring line.
>
>
>
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