Hi Todd thanks for your response.
On Tue, Aug 4, 2020 at 11:01 AM Todd <toddr...@gmail.com> wrote:
> On Tue, Aug 4, 2020 at 8:17 AM Ricky Teachey <ri...@teachey.org> wrote:
>
>> ...
>>
>> There could be several reasons for changing the item dunder signatures.
>> The immediate reason is making the intuition around how to add kwd arg
>> support to square brackets more obvious and sane.
>>
>> A second reason is it might be more intuitive for users who have to learn
>> and remember that multiple arguments to [ ] get packed into a tuple, but
>> this doesn't happen anywhere else.
>>
>
> My main issue with this is that, in my opinion, dunders are not something
> a beginner should be messing with anyway. By the time someone is
> experienced enough to start working on this, they are also experienced
> enough to understand that special cases like this exist for historical
> reasons.
>
Yeah I understand and agree but even non-beginners benefit a lot from
having consistent behaviors in the language, and not having to remember
exceptions.
As for my specific idea of how to accomplish the signature change, it's
true that adding replacement getx/setx/delx dunders to the language would
in fact be *additional* things to remember, not *fewer *things. But the
goal would be to eventually replace getitem/setitem/delitem-- so this would
be a temporary situation and eventually go away. Similar to how most people
don't have a daily need to remember any number of old, previously standard
and important, ways of doing things after a few years of transition.
> Another reason: it could make writing code for specialized libraries
> that tend to abuse (for the good of us all!) item dunders, like pandas,
> much easier. Right now such libraries have to rely on their own efforts to
> break up a key:
>
>>
>> def __getitem__(self, key):
>> try:
>> k1, k2 = key
>> except TypeError:
>> raise TypeError("two tuple key required")
>>
>> But for regular function calls (as opposed to item getting) we get to
>> write our signature however we want and rely on the language to handle all
>> of this for us:
>>
>> def f(k1, k2):
>> # no worries about parsing out the arguments
>>
>
> But this is still a pretty simple piece of code. Is it worth having
> everyone start over from scratch to avoid dealing with 4 lines of code?
> Especially since knowing the number of indices ahead of time is a special
> case for a small number of projects like pandas. In most cases, the number
> of indices cannot be known until runtime, so this would provide no
> practical benefit for most projects.
>
>
This alone wouldn't be enough of a benefit, I agree. I find the combined
benefits taken together compelling enough to at least warrant the
exploration.
> -----------
>>
>> One idea: change the "real" names of the dunders. Give `type` default
>> versions of the new dunders that direct the call to the old dunder names.
>> ...
>>
>> However the set dunder signature would be a problem, because to mirror
>> the current behavior we end up writing what is now a syntax error:
>>
>> def __setx__(self, /, *__key, __value, **__kwargs):
>> self.__setitem__(__key, __value, **__kwargs)
>>
>> The intended meaning above would be that the last positional argument
>> gets assigned to __value. Maybe someone could suggest a way to fix this.
>>
>
> The simplest way would be to put "value" first:
>
> def __setx__(self, __value, /, *__key, **__kwargs):
>
I didn't mention that as an option because-- since we are dealing with
positional only arguments much of the time-- it could become very confusing
to switch the order of the key and value arguments in actual code.
But if that is the case then the __setx__ hurdle appears insurmountable,
apart from modifying the language so that function signatures can behave
similar to this syntax feature:
first, *rest, last = [1, 2, 3, 4, 5, 6]
assert first == 1
assert last == 6
assert rest == [2, 3, 4, 5]
... so then you could write a function signature in this way:
def f(first, *rest, last, /):
return first, rest, last
first, rest, last = f(1, 2, 3, 4, 5, 6)
assert first == 1
assert last == 6
assert rest == [2, 3, 4, 5]
So I suppose that would be yet another change that would need to happen
first.
---
Ricky.
"I've never met a Kentucky man who wasn't either thinking about going home
or actually going home." - Happy Chandler
_______________________________________________
Python-ideas mailing list -- python-ideas@python.org
To unsubscribe send an email to python-ideas-le...@python.org
https://mail.python.org/mailman3/lists/python-ideas.python.org/
Message archived at
https://mail.python.org/archives/list/python-ideas@python.org/message/SJLSHJSOVOIYOXQ2BMUC52AES6ZBIAUX/
Code of Conduct: http://python.org/psf/codeofconduct/
