[Numpy-discussion] Python 3 dict support (issue #5718)

[Jaime Fernández del Río]

On Wed, Jul 20, 2016 at 9:39 PM, Hannah <story645 at gmail.com> wrote:

> I second (and third & fourth &...) this
>
> Thanks so much for this, Jaime, it's exactly what I was looking for and
> couldn't find. Maybe this can be linked to in the contribute docs as an
> "orienting yourself in the codebase" page?
>
Glad to know it helped, realizing how this works was one of the big leaps
in understanding the code base for myself too.  We (my wife and I) have
sent the kids on vacation with their grandparents, so when we are done
enjoying our shortly recovered freedom hunting for Pokemons around Zurich,
I'll try to find time to write this up in a form suitable for the docs,
hopefully over the next couple of weeks.

I have been known to not keep commitments like this in the past, so don't
hold your breath just in case...

Jaime


>
> On Wed, Jul 20, 2016 at 11:07 AM, Joseph Fox-Rabinovitz <
> jfoxrabinovitz at gmail.com> wrote:
>
>> Jaime,
>>
>> This is a great intro for people looking to jump into the C side of
>> things. I have been trying to figure out which bits are the important
>> ones from looking at the code and the docs. Your post cut out most of
>> the confusion. Is there some way you would consider adding something
>> like this this to the docs?
>>
>>     -Joe
>>
>>
>> On Wed, Jul 20, 2016 at 8:52 AM, Jaime Fernández del Río
>> <jaime.frio at gmail.com> wrote:
>> > On Wed, Jul 20, 2016 at 4:28 AM, Hannah <story645 at gmail.com> wrote:
>> >>
>> >> Hi,
>> >> I started venturing down the rabbit hole of trying to write a patch to
>> add
>> >> support for numpy to convert python 3 dictionary keys
>> >> (collections.abc.ViewMapping objects), which is open issue #5718 and am
>> >> having trouble orienting myself. I'm unclear as to where the python
>> entry
>> >> point into array is (basically, what function np.array drops into and
>> if
>> >> this is in Python or C) and where/what language (fine with writing
>> either) a
>> >> patch that supports MappingViews would go. Any help getting oriented
>> would
>> >> be much appreciated.
>> >
>> >
>> > Hi Hannah,
>> >
>> > ǹp.array is written in C, and is part of the multiarray module that is
>> > defined here:
>> >
>> >
>> https://github.com/numpy/numpy/blob/maintenance/1.11.x/numpy/core/src/multiarray/multiarraymodule.c
>> >
>> > The "array" name is mapped here:
>> >
>> >
>> https://github.com/numpy/numpy/blob/maintenance/1.11.x/numpy/core/src/multiarray/multiarraymodule.c#L4093
>> >
>> > to the function _array_fromobject defined here:
>> >
>> >
>> https://github.com/numpy/numpy/blob/maintenance/1.11.x/numpy/core/src/multiarray/multiarraymodule.c#L1557
>> >
>> > That functions does some checking and has a couple of fast paths for the
>> > case where the input is already an array or a subclass, but for the
>> general
>> > case it relies on PyArray_CheckFromAny:
>> >
>> >
>> https://github.com/numpy/numpy/blob/maintenance/1.11.x/numpy/core/src/multiarray/ctors.c#L1848
>> >
>> > which in turn calls Pyarray_FromAny:
>> >
>> >
>> https://github.com/numpy/numpy/blob/maintenance/1.11.x/numpy/core/src/multiarray/ctors.c#L1674
>> >
>> > You will also haveto take a look at what goes on in
>> > PyArray_GetArrayParamsFromObject, which gets called by PyArray_FromAny;
>> >
>> >
>> https://github.com/numpy/numpy/blob/maintenance/1.11.x/numpy/core/src/multiarray/ctors.c#L1428
>> >
>> > as well as several other places, but I think they are all (or most of
>> them)
>> > in ctors.c.
>> >
>> > You may also want to take a llok at PyArray_FromIter, which is the
>> function
>> > that ultimately takes care of calls to np.fromiter:
>> >
>> >
>> https://github.com/numpy/numpy/blob/maintenance/1.11.x/numpy/core/src/multiarray/ctors.c#L3657
>> >
>> > It's messy, but not that bad once you get used to it: good luck!
>> >
>> > Jaime
>> >
>> >>
>> >>
>> >> The reasoning for the patch is s that dicts are one of the most common
>> >> Python datatypes and this specifically is because of an upstream issue
>> of
>> >> wanting dict support in matplotlib.
>> >>
>> >> Thanks,
>> >> Hannah
>> >>
>> >> _______________________________________________
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>> >>
>> >
>> >
>> >
>> > --
>> > (\__/)
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>> > dominación mundial.
>> >
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