On Thu, Feb 18, 2016 at 10:15 AM, Antony Lee <antony....@berkeley.edu> wrote:
> Mostly so that there is no performance lost when someone passes range(...) > instead of np.arange(...). At least I had never realized that one is much > faster than the other and always just passed range() as a convenience. > Well, pretty much everything in numpy is faster if you use the numpy array version rather than plain python -- this hardly seems like the extra code would be worth it. numpy's array() constructor can (and should) take an arbitrary iterable. It does make some sense that you we might want to special case iterators, as you don't want to loop through them too many times, which is what np.fromiter() is for. and _maybe_ it would be worth special casing python lists, as you can access items faster, and they are really, really common (or has this already been done?), but special casing range() is getting silly. And it might be hard to do. At the C level I suppose you could actually know what the parameters and state of the range object are and create an array directly from that -- but that's what arange is for... -CHB > 2016-02-17 10:50 GMT-08:00 Chris Barker <chris.bar...@noaa.gov>: > >> On Sun, Feb 14, 2016 at 11:41 PM, Antony Lee <antony....@berkeley.edu> >> wrote: >> >>> So how can np.array(range(...)) even work? >>> >> >> range() (in py3) is not a generator, nor is is a iterator. it is a range >> object, which is lazily evaluated, and satisfies both the iterator protocol >> and the sequence protocol (at least most of it: >> >> In [*1*]: r = range(10) >> >> >> In [*2*]: r[3] >> >> Out[*2*]: 3 >> >> >> In [*3*]: len(r) >> >> Out[*3*]: 10 >> >> >> In [*4*]: type(r) >> >> Out[*4*]: range >> >> In [*9*]: isinstance(r, collections.abc.Sequence) >> >> Out[*9*]: True >> >> In [*10*]: l = list() >> >> In [*11*]: isinstance(l, collections.abc.Sequence) >> >> Out[*11*]: True >> >> In [*12*]: isinstance(r, collections.abc.Iterable) >> >> Out[*12*]: True >> I'm still totally confused as to why we'd need to special-case range when >> we have arange(). >> >> -CHB >> >> >> >> -- >> >> Christopher Barker, Ph.D. >> Oceanographer >> >> Emergency Response Division >> NOAA/NOS/OR&R (206) 526-6959 voice >> 7600 Sand Point Way NE (206) 526-6329 fax >> Seattle, WA 98115 (206) 526-6317 main reception >> >> chris.bar...@noaa.gov >> >> _______________________________________________ >> NumPy-Discussion mailing list >> NumPy-Discussion@scipy.org >> https://mail.scipy.org/mailman/listinfo/numpy-discussion >> >> > > _______________________________________________ > NumPy-Discussion mailing list > NumPy-Discussion@scipy.org > https://mail.scipy.org/mailman/listinfo/numpy-discussion > > -- Christopher Barker, Ph.D. Oceanographer Emergency Response Division NOAA/NOS/OR&R (206) 526-6959 voice 7600 Sand Point Way NE (206) 526-6329 fax Seattle, WA 98115 (206) 526-6317 main reception chris.bar...@noaa.gov
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