On Dec 3, 2019, at 17:47, Oscar Benjamin <oscar.j.benja...@gmail.com> wrote:
>
> On Tue, 3 Dec 2019 at 12:48, Paul Moore <p.f.mo...@gmail.com> wrote:
>>
>> My impression is that he was asking for a re.findfirst(...) function
>> to give a more discoverable name to the next(re.finditer((...)) idiom.
>>
>> As a single example of defining a dedicated function to replace a
>> one-liner, I think it's marginal at best (although discoverability
>> *is* important here). But IMO it is true that using
>> next(some_iterator) to mean "get the first value returned" is
>> something that's needed relatively frequently, but often overlooked by
>> people. I'm not sure there's a good solution, though - adding an alias
>> first() for "next() when used to get the first element" is probably
>> overkill, and apart from dedicated syntax, it would be hard to find
>> something much shorter than next().
>>
>> Maybe it's just an education issue, people aren't sufficiently
>> familiar with the idiom?
>
> What exactly is the idiom here?
The OP’s proposal was for a findfirst function that takes a mandatory default
value. So presumably the idiom is just next with a default value:
def findfirst(pattern, text, default):
return next(finditer(pattern, text), default)
And this “first or default” thing is pretty common, not just restricted to the
OP’s use case, and next already handles it perfectly, but apparently not enough
people know about it.
> Using bare next is not a good idea because it leaks StopIteration
> which can have awkward side effects.
Not the two-argument form.
> So are you suggesting something
> like
>
> result = next(re.finditer(...), None)
> if result is None:
> # raise or something
> else:
> # use result
Using None as a sentinel would work here, but as a generic idiom it’s not a
good habit, because plenty of other functions can validly iterate None.
> I would be in favour of adding an alternative to next that raises a
> different exception when the result isn't found.
If you need that, it’s pretty trivial to write yourself.
If you think other people need it and don’t know how to write it, why not
submit it to more-itertools and/or tools? If it gets enough uptake, you can
always suggest adding it to itertools, or even modifying next to take a keyword
argument or something.
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