I don't like consuming the iterator in the exception case. You might expect just one, but have a fallback approach for more. You could build the safer behavior using itertools.tee() or itertools.chain().
On Mon, Jul 27, 2020, 3:10 PM Noam Yorav-Raphael <noamr...@gmail.com> wrote: > Hi, > > There's a simple function that I use many times, and I think may be a good > fit to be added to itertools. A function that gets an iterator, and if it > has exactly one element returns it, and otherwise raises an exception. This > is very useful for cases where I do some sort of query that I expect to get > exactly one result, and I want an exception to be raised if I'm wrong. For > example: > > jack = one(p for p in people if p.id == '1234') > > sqlalchemy already has such a function for queries: > https://docs.sqlalchemy.org/en/13/orm/query.html#sqlalchemy.orm.query.Query.one > > This is my implementation: > > def one(iterable): > it = iter(iterable) > try: > r = next(it) > except StopIteration: > raise ValueError("Iterator is empty") > try: > next(it) > except StopIteration: > return r > else: > raise ValueError("Iterator has more than one item") > > What do you think? > > Thanks, > Noam > _______________________________________________ > Python-Dev mailing list -- python-dev@python.org > To unsubscribe send an email to python-dev-le...@python.org > https://mail.python.org/mailman3/lists/python-dev.python.org/ > Message archived at > https://mail.python.org/archives/list/python-dev@python.org/message/D52MPKLIN4VEXBOCKVMTWAK66MAOEINY/ > Code of Conduct: http://python.org/psf/codeofconduct/ >
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