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

[Joseph Fox-Rabinovitz]

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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