A proposal to make map() not return an iterator seems like a non-starter. Yes, Python 2 worked that way, but that was a long time ago and we know better now.
In the simple example it doesn't matter much: mo = map(lambda x: x, "aardvark") But map() is more useful for the non-toy case: mo = map(expensive_db_lookup, list_of_keys) list_of_keys can be a concrete list, but I'm using map() mainly specifically to get lazy iterator behavior. On Sat, Dec 1, 2018, 11:10 AM Paul Svensson <paul-pyt...@svensson.org wrote: > On Sat, 1 Dec 2018, Steven D'Aprano wrote: > > > On Thu, Nov 29, 2018 at 08:13:12PM -0500, Paul Svensson wrote: > > > >> What's being proposed is simple, either: > >> * len(map(f, x)) == len(x), or > >> * both raise TypeError > > > > Simple, obvious, and problematic. > > > > Here's a map object I prepared earlier: > > > > from itertools import islice > > mo = map(lambda x: x, "aardvark") > > list(islice(mo, 3)) > > > > If I now pass you the map object, mo, what should len(mo) return? Five > > or eight? > > mo = "aardvark" > list(islice(mo, 3)) > > By what magic would the length change? > Per the proposal, it can only be eight. > Of course, that means mo can't, in this case, be an iterator. > That's what the proposal would change. > > /Paul > _______________________________________________ > Python-ideas mailing list > Python-ideas@python.org > https://mail.python.org/mailman/listinfo/python-ideas > Code of Conduct: http://python.org/psf/codeofconduct/ >
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