This seems like it might be a reasonable thing to have in intertools? It's not hard to write this sort of thing with map:
some_iter = map(lambda x: (print(x), x)[1], some_iter) But it's a little awkward. (Though maybe I'm missing a less awkward way to do that.) Java has Stream.peek for similar functionality, while Stream.forEach is analogous to Python's map. On Sun, Oct 25, 2020 at 9:02 AM <anderssonpub...@gmail.com> wrote: > Python has many tools for iteration, such as map and filter, that change > an iterator into another iterator without consuming the iterator. These > make it simple to deal with many items in a list without consuming > excessive memory. > > Occasionally it is useful to be able to tap into iterator items and > execute a function (such as a side effect to validate elements or print > them) without making any changes to the overall iterator. This is similar > to the idea of a tap in rxjs: > https://rxjs-dev.firebaseapp.com/api/operators/tap. > > The proposed interface would be: > def generate_items() -> list[int]: > some_iter = range(10) > some_iter = tap(assert_int, some_iter) > some_iter = tap(print, some_iter) > return list(some_iter) > > This would be useful to (for example): > 1. Debug chained iterators without a debugger (at the moment you would > have to convert the list and then print the whole list or include a print > statement in one of the chained functions) > 2. Check that items in an iterator conform to assumptions and raising > exceptions if they do not > 3. Improve type hints in editors since after the assert is executed all > items conform to the assert in the tap (for example, they are an integer) > > The implementation would be quite simple (at least in python): > def tap(func: typing.Callable[[T], typing.Any], iter: typing.Iterable[T]) > -> typing.iterable[T]: > for item in iter: > func(item) > yield item > > Thoughts? > _______________________________________________ > Python-ideas mailing list -- python-ideas@python.org > To unsubscribe send an email to python-ideas-le...@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/7Q3NR4SKUC72PVQ3APK2HL2HNX3HP2IE/ > Code of Conduct: http://python.org/psf/codeofconduct/ >
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