+1 for itertools.first(seq, default=Exception) *and* itertools.one(seq, default=Exception) This is a very common pattern (particularly with RDF / JSON-LD (@type) where there can be multiple instances of any predicate-object / attribute-value pair) SQLAlchemy also has .first(), .one(), and .one_or_none() (with no default= and sqlalchemy.orm.exc.NoResultFound and sqlalchemy.orm.exc.MultipleResultsFound) On Sat, Dec 7, 2019, 9:20 AM Kirill Balunov <kirillbalunov@gmail.com> wrote:
сб, 7 дек. 2019 г. в 03:45, Steven D'Aprano <steve@pearwood.info>:
This is how I would implement the function in Python:
def first(iterable, default=None): return next(iter(iterable), default)
A somewhat related discussion was somewhere inside November 2017 <https://mail.python.org/archives/list/python-ideas@python.org/thread/QX6IRM4...> thread "How assignment should work with generators?". The main idea was to extend assignment syntax to something like `first, second, ... = gen` which should be equivalent to `first, second, ... = next(gen), next(gen)`. Another idea was (but nobody liked it) to change the behavior of `x, y, *tail = iter` to not to consume starred part and to make a generator instead of list. I understand that the topic discussed here is slightly different, but in my understanding it is all the eggs of one chicken.
I still like the idea of partial assignment syntax `x, y, ... = iter` but as well as then, I understand that I don’t have enough English knowledge and time to write a proposal on that topic and especially to follow thread and to defend an idea :( The main objection was that this all is easy achievable with `islice` from `itertools`.
Back to the topic - maybe `first` is a good citizen for `itertools` module. Because this idea (about first ) is discussed constantly every two years.
with kind regards, -gdg _______________________________________________ Python-ideas mailing list -- python-ideas@python.org To unsubscribe send an email to python-ideas-leave@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/D7ALA5... Code of Conduct: http://python.org/psf/codeofconduct/