[Python-ideas] Start argument for itertools.accumulate() [Was: Proposal: A Reduce-Map Comprehension and a "last" builtin]

[Guido van Rossum]

Well if you can get Raymond to agree on that too I suppose you can go
ahead. Personally I'm -0 but I don't really write this kind of algorithmic
code enough to know what's useful. I do think that the new parameter name
is ugly. But maybe that's the point.

On Sat, Apr 7, 2018 at 10:26 PM, Tim Peters <tim.peters at gmail.com> wrote:

> Top-posting just to say I agree with Nick's bottom line (changing the
> name to `first_result=`).  I remain just +0.5, although that is up a
> notch from yesterday's +0.4 ;-)
>
> --- nothing new below ---
>
> On Sun, Apr 8, 2018 at 12:19 AM, Nick Coghlan <ncoghlan at gmail.com> wrote:
> > On 8 April 2018 at 14:31, Guido van Rossum <guido at python.org> wrote:
> >> Given that two respected members of the community so strongly disagree
> >> whether accumulate([], start=0) should behave like accumulate([]) or
> like
> >> accumulate([0]), maybe in the end it's better not to add a start
> argument.
> >> (The disagreement suggests that we can't trust users' intuition here.)
> >
> > The potential ambiguity I see is created mainly by calling the
> > proposed parameter "start", while having it do more than just adjust
> > the individual partial sum calculations by adding an extra partial
> > result to the output series.
> >
> > If it's called something else (e.g. "first_result"), then the
> > potential "sum(iterable, start=start)" misinterpretation goes away,
> > and it can have Tim's desired effect of defining the first output
> > value (effectively prepending it to the input iterable, without the
> > boilerplate and overhead of actually doing so).
> >
> > A name like "first_result" would also make it clearer to readers that
> > passing that parameter has an impact on the length of the output
> > series (since you're injecting an extra result), and also that the
> > production of the first result skips calling func completely (as can
> > be seen in Tim's str coercion example).
> >
> > So where I'd be -1 on:
> >
> >     >>> list(accumulate(1, 2, 3))
> >     [1, 3, 6]
> >     >>> list(accumulate(1, 2, 3, start=0))
> >     [0, 1, 3, 6]
> >     >>> list(accumulate(1, 2, 3, start=1))
> >     [1, 2, 4, 7]
> >
> > I'd be +1 on:
> >
> >     >>> list(accumulate(1, 2, 3))
> >     [1, 3, 6]
> >     >>> list(accumulate(1, 2, 3, first_result=0))
> >     [0, 1, 3, 6]
> >     >>> list(accumulate(1, 2, 3, first_result=1))
> >     [1, 2, 4, 7]
> >
> > Cheers,
> > Nick.
> >
> > --
> > Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
>



-- 
--Guido van Rossum (python.org/~guido)
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