I would think that you can use tuple unpacking for this? single_element, = some_iterator
Will attempt to unpack the some_iterator into single_element and fail if single_element doesn't have exactly 1 element. It also has the added benefit that it works for any number of elements: one, two = some_iterator Example: >>> a = [1] >>> one, = a >>> one 1 >>> b = [1, 2] >>> one, = b --------------------------------------------------------------------------- ValueError Traceback (most recent call last) <ipython-input-5-9b70ee0300f5> in <module> ----> 1 one, = b ValueError: too many values to unpack (expected 1) >>> c = [] >>> one, = c --------------------------------------------------------------------------- ValueError Traceback (most recent call last) <ipython-input-7-413c1b218942> in <module> ----> 1 one, = c ValueError: not enough values to unpack (expected 1, got 0) Best, Paul On 7/27/20 3:19 PM, Rollo Konig-Brock wrote: > I second this as being useful. > > However the “pythonic” way (whatever that means nowadays) is to do a > for break else loop, which I think is kinda difficult to read as you > need to make a few assumptions. > > Rollo > >> On 27 Jul 2020, at 20:06, 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 <http://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/ > > _______________________________________________ > 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/3NA4E3QCTSLGIQXAMVWUL66TK6O7ZHLS/ > Code of Conduct: http://python.org/psf/codeofconduct/
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