Paul Rubin <no.em...@nospam.invalid> writes:
> Steven D'Aprano <steve+comp.lang.pyt...@pearwood.info> writes:
>> Apart from this horrible idiom:
>>
>> def func(iterable):
>> it = iter(iterable)
>> failed = False
>> try:
>> x = next(it)
>> except StopIteration:
>> failed = True
>> if failed:
>> raise ValueError("can't process empty iterable")
>> print(x)
>>
>>
>> or similar, is there really no way to avoid these chained exceptions?
>
> Seems like yet another example of people doing messy things with
> exceptions that can easily be done with iterators and itertools:
>
> from itertools import islice
>
> def func(iterable):
> xs = list(islice(iter(iterable), 1))
> if len(xs) == 0:
> raise ValueError(...)
> print xs[0]
>
> It's really unfortunate, though, that Python 3 didn't offer a way to
> peek at the next element of an iterable and test emptiness directly.
I missed the start of this discussion but there are two simpler ways:
def func(iterable):
for x in iterable:
print(x)
return
raise ValueError("... empty iterable")
Or using 3.x's next's optional second argument:
_nonext=object()
def func(iterable):
x = next(iter(iterable), _nonext)
if x is _nonext:
raise ValueError("... empty iterable")
print(x)
--
Arnaud
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