[Numpy-discussion] Suggestion: special-case np.array(range(...)) to be faster

[josef.pktd at gmail.com]

On Thu, Feb 18, 2016 at 1:15 PM, Antony Lee <antony.lee at 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.
>
> Antony
>
> 2016-02-17 10:50 GMT-08:00 Chris Barker <chris.barker at noaa.gov>:
>
>> On Sun, Feb 14, 2016 at 11:41 PM, Antony Lee <antony.lee at 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)
>>
>
thanks, I didn't know that

the range r here doesn't get eaten by iterating through it
while
r = (i for i in range(5))
is only good for a single pass.

(tried on python 3.4)

Josef



>
>> 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
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>>
>> Chris.Barker at noaa.gov
>>
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>
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