Mailman 3 July 2019 - NumPy-Discussion

NumPy Community Meeting Wednesday, July 17
by Sebastian Berg 16 Jul '19

16 Jul '19

Hi all, There will be a NumPy Community meeting Wednesday July 17 at 11 am Pacific Time. Everyone is invited to join in and edit the work-in- progress meeting topics and notes: https://hackmd.io/76o-IxCjQX2mOXO_wwkcpg Best wishes Sebastian

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Creating a subclass that never propagates
by Kevin Sheppard 16 Jul '19

16 Jul '19

I am trying to make a subclass that never propagates so that when interacted with another ndarray, or even itself so that the return type is always ndarray. Is this possible? I got pretty far with def __array_wrap__(self, out_arr, context=None): if out_arr.shape == (): return out_arr.item() # if ufunc output is scalar, return it else: out = super(ArrayLike, self).__array_wrap__(out_arr, context) # Never return ArrayLike if isinstance(out, ArrayLike): out = out.view(np.ndarray) return out Which works well for ufuncs. However, when I try other functions like `dot` I get my subclass type returned. If there a reasonable way to ensure that my subclass doesn't propagate? I think I would need some way to override the behavior when .view(MySubClass) is called. Thanks, Kevin

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defining a NumPy API standard?
by Ralf Gommers 16 Jul '19

16 Jul '19

Hi all, I have an idea that I've discussed with a few people in person, and the feedback has generally been positive. So I'd like to bring it up here, to get a sense of if this is going to fly. Note that this is NOT a proposal at this point. Idea in five words: define a NumPy API standard Observations ------------ - Many libraries, both in Python and other languages, have APIs copied from or inspired by NumPy. - All of those APIs are incomplete, and many deviate from NumPy either by accident or on purpose. - The NumPy API is very large and ill-defined. Libraries with a NumPy-like API ------------------------------- In Python: - GPU: Tensorflow, PyTorch, CuPy, MXNet - distributed: Dask - sparse: pydata/sparse - other: tensorly, uarray/unumpy, ... In other languages: - JavaScript: numjs - Go: Gonum - Rust: rust-ndarray, rust-numpy - C++: xtensor - C: XND - Java: ND4J - C#: NumSharp, numpy.net - Ruby: Narray, xnd-ruby - R: Rray This is an incomplete list. Xtensor and XND aim for multi-language support. These libraries are of varying completeness, size and quality - everything from one-person efforts that have just started, to large code bases that go beyond NumPy in features or performance. Idea ---- Define a standard for "the NumPy API" (or "NumPy core API", or .... - it's just a name for now), that other libraries can use as a guide on what to implement and when to say they are NumPy compatible. In scope: - Define a NumPy API standard, containing an N-dimensional array object and a set of functions. - List of functions and ndarray methods to include. - Recommendations about where to deviate from NumPy (e.g. leave out array scalars) Out of scope, or to be treated separately: - dtypes and casting - (g)ufuncs - function behavior (e.g. returning views vs. copies, which keyword arguments to include) - indexing behavior - submodules (fft, random, linalg) Who cares and why? - Library authors: this saves them work and helps them make decisions. - End users: consistency between libraries/languages, helps transfer knowledge and understand code - NumPy developers: gives them a vocabulary for "the NumPy API", "compatible with NumPy", etc. Risks: - If not done well, we just add to the confusion rather than make things better. - Opportunity for endless amount of bikeshedding - ? Some more rationale: We (NumPy devs) mostly have a shared understanding of what is "core NumPy functionality", what we'd like to remove but are stuck with, what's not used a whole lot, etc. Examples: financial functions don't belong, array creation methods with weird names like np.r_ were a mistake. We are not communicating this in any way though. Doing so would be helpful. Perhaps this API standard could even have layers, to indicate what's really core, what are secondary sets of functionality to include in other libraries, etc. Discussion and next steps ------------------------- What I'd like to get a sense of is: - Is this a good idea to begin with? - What should the scope be? - What should the format be (a NEP, some other doc, defining in code)? If this idea is well-received, I can try to draft a proposal during the next month (help/volunteers welcome!). It can then be discussed at SciPy'19 - high-bandwidth communication may help to get a set of people on the same page and hash out a lot of details. Thoughts? Ralf

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converting 1 dimensional array to 2 dimensional array
by Omry Levy 15 Jul '19

15 Jul '19

Hi All, I know how to reshape arrays, my problem is a little more complicated than that. I am looking for the most efficient way to do the following and an example will help: 1) I have a an array of bytes b = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12] This bytes array represents a width of 2 and a height of 3. Each 2 bytes in that bytes array makes an unsigned 16 bit integer. 2) I want to get the following 2 dimensional array from the bytes array where each item in the two dimensional array is an unsigned 16 bit integer something like: [ [(1,2) , (3,4)], [(5,6) , (7,8)], [(9,10) , (11,12)] ] in the first row there are 2 elements each one is made of 2 bytes from the bytes array etc... meaning that (1, 2) = b[0] + b[1] << 8 (3, 4) = b[2] + b[3] << 8 ... ... What is the most efficient way to achieve that with numpy ? Thanks 0L [1] << 8 ,[2], [3, 4]

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Kriti (our Outreachy intern) has published a blog post about being accepted to the program
by Matti Picus 15 Jul '19

15 Jul '19

https://github.com/kritisingh1/numpy/wiki/Now-You-Know-It! Worth a read, see what applicants go through to get accepted. Feel free to re-publish it. There will be more coming as she progresses through the summer.

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Developer Meeting @SciPy Conference, Friday 1pm
by Sebastian Berg 12 Jul '19

12 Jul '19

Hi all, we have reserved a room for a Developer meeting at SciPy. The meeting is planned for Friday at 1pm in room 108. I have created a tentative Agenda with some broad discussion points at: https://hackmd.io/rg0DI0JASKeZ_G5bTJ3YSA Please feel free to edit or add the Agenda. All the Best, Sebastian

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float16 but no complex32?
by Neal Becker 11 Jul '19

11 Jul '19

I see a float16 dtype but not complex32. Is this an oversight? Thanks, Neal -- Those who don't understand recursion are doomed to repeat it

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Adding a "suffle=True" kwarg to numpy.random.Generator.choice
by Matti Picus 10 Jul '19

10 Jul '19

In PR https://github.com/numpy/numpy/pull/13812, Thrasibule rewrote the algorithm used with a faster alternative branch for some cases. The faster algorithm does not necessarily shuffle the results, so for instance gen.choice(2000, 2000, replace=False) may simply return arange(2000). In the old code the result is always shuffled. We propose adding a new kwarg "shuffle" that defaults to True. Users looking for maximum performance may choose to use shuffle=False. Since this is a behavioral change (although only in the new Generator class, the new code will not be used in RandomState), we are proposing it to the mailing list Any thoughts? Matti

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No Community Meeting this Week
by Sebastian Berg 08 Jul '19

08 Jul '19

Hi all, due to the SciPy conference we will _not_ have a Community meeting this week. We will have a developer meeting at the SciPy conference on Friday at 1pm in room 108 and take part in the Sprints. I will send a tentative Agenda/things to discuss in a separate email. Best, Sebastian

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Regarding adding new function in Numpy
by ANURAG ANURAG 08 Jul '19

08 Jul '19

Sir, I was recently converting some Matlab codes into python, where I recently stumble upon bitget(n,x) function of Matlab, b = bitget(A,bit) returns the bit value at the position bit in integer array A. I was unable to find any Numpy equivalent of this, so should I create a pull request in Numpy for the same! Regards, Anurag

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