On Wed, Jun 16, 2021 at 8:04 PM David Mertz <me...@gnosis.cx> wrote: > Flattening nested lists is not uncommon. And yes sum seemed the natural >> way to do it at the time. >> > > I remember the discussion in 2013 about the quadratic performance of > summing strings. There were proposals for optimization of the string case, >
IIUC, the idea behind raising, rather than optimizing, is that there is a "better" way to do it, and it's a good lesson. After all, sum() aside, we also want to discourage folks from doing a lot of string concatenation in a loop as well. I'm sympathetic to raising an exception on `sum(list_of_lists)` similar to > `sum(list_of_strings)`. But what exactly is the recommended substitute? > We have this: > > list(chain.from_iterable(list_of_lists)) > > Which is pretty nice, and what I'd probably do, but it DOES require > importing from itertools to use it. That feels like a drawback, at least a > minor one. > I agree -- str.join() is built in and really idiomatic Python -- itertools.chain is, I suppose idiomatic Python, but there's the import, a lot of extra typing, and a substantial cognitive load to figure it out the first (few) times you use it. (I don't think I ever have...) If, as suggested, flattening a list of lists is a common operation, a nice clean and efficient built in way to do it would be reasonable. Heck, you could make it a list method :-) If you read the BPO the OP linked, that was a suggested patch to optimize sum(list_of_lists) -- I'm not sure that's such a bad idea after all. -CHB NOTE: One reason I've never had to flatten a list of lists is because I'm a heavy numpy user -- I'd be more likely to have an ndarray and flatten that -- which is very easy and efficient :-) -- Christopher Barker, PhD (Chris) Python Language Consulting - Teaching - Scientific Software Development - Desktop GUI and Web Development - wxPython, numpy, scipy, Cython
_______________________________________________ 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/T5UUKFQXARJ34YIERO7AFS4FBRP6QIEJ/ Code of Conduct: http://python.org/psf/codeofconduct/
