New submission from flying sheep: Things like progressbars want len() to work on iterated objects.
It’s possible to define __len__ for many of the iterables returned by itertools. some arguments have to be iterated to find the len(): of course we have to check if those are reentrant, and raise a TypeError if they are non-reentrant. (signified by “(r)→”) for the predicate functions, it’s questionable if we should offer it, since they might take a long time and “len” is a property-like function that feels like it should return fast. map(func, iterable) → len(iterable) count(), cycle(), repeat() → infinty, but because len() returns integers, and there’s only float infinity, that’s impossible accumulate(iterable) → len(iterable) chain(*iterables) → sum(len(it) for it in iterables) chain.from_iterable(iterables) (r)→ like the above compress(data, selectors) (r)→ sum(1 for s in selectors if s) dropwhile(pred, iterable) (r)→ for skip, r in enumerate(map(pred, iterable)): if r: return len(iterable) - skip filterfalse(pred, iterable) (r)→ sum(1 for r in map(pred, iterable) if r) groupby(iterable[, keyfunc]) (r)→ no way but to actually execute it all islice(seq, [start,] stop [, step]) → calculatable if len(seq) is possible starmap(function, iterables) → len(iterables) takewhile(pred, iterable) (r)→ for skip, r in enumerate(map(pred, iterable)): if not r: return skip tee(iterable[, n]) → n zip_longest(*iterables[, fillvalue]) (r)→ max(len(it) for it in iterables) product(), permutations(), combinations(), combinations_with_replacement() → there’s math for that. ---------- components: Library (Lib) messages: 248451 nosy: flying sheep priority: normal severity: normal status: open title: Add __len__ to map, everything in itertools type: enhancement versions: Python 3.6 _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue24849> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
