Re: [Numpy-discussion] Using the C-API iterator with object arrays
Hi Jaime On Mon, 2018-02-12 at 12:56 +, Jaime Fernández del Río wrote: > On Mon, Feb 12, 2018 at 12:13 PM Eugen Wintersberger r...@gmail.com> wrote: > > > > > > > > > > > > > Hi there, > > > > I have a question concerning the numpy iterator C-API. I want to > > create a numpy > > > > string array using NPY_OBJECT as a datatype for creating the array > > (the reason I am going for this > > > > approach is that I do not know the length of the individual strings > > at the time I construct > > > > the array, I only know its shape). The original strings are stored > > > > I think you have the indirections wrong in dataptr? You are absolutely right. Now everything works just as it should. Thanks a lot. > NpyIter_GetDataPtrArray returns a char**, that hold the address of > the variable where the iterator holds the address of the first byte > of the current item being iterated. > When you write to dataptr[0] you are not writing to the array, but to > where the iterator holds the address of the first byte of the current > item. > So you would have to write to dataptr[0][0], or **dataptr, to > actually affect the contents of the array. Of course, > your dataptr being a PyObject**, the compiler would probably > complaint about such an assignment. > I think that if you define dataptr as a PyObject*** (yay, three star > programming!) and then assign to **dataptr, everything will work > fine. If that doesn't work, maybe try to make dataptr a char**, and > then assign to (PyObject *)(**dataptr) = ... > Jaime > > > Thanks in advance. > > > > > > > > best regards > > > > Eugen > > > > > > ___ > > > > NumPy-Discussion mailing list > > > > NumPy-Discussion@python.org > > > > https://mail.python.org/mailman/listinfo/numpy-discussion > > > > > > > -- > (\__/) > ( O.o) > ( > <) Este es Conejo. Copia a Conejo en tu firma y ayúdale en sus > planes de dominación mundial. > > ___ > NumPy-Discussion mailing list > NumPy-Discussion@python.org > https://mail.python.org/mailman/listinfo/numpy-discussion signature.asc Description: This is a digitally signed message part ___ NumPy-Discussion mailing list NumPy-Discussion@python.org https://mail.python.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] Using the C-API iterator with object arrays
On Mon, Feb 12, 2018 at 6:13 AM, Eugen Wintersberger <
eugen.wintersber...@gmail.com> wrote:
> Hi there,
> I have a question concerning the numpy iterator C-API. I want to create a
> numpy
> string array using NPY_OBJECT as a datatype for creating the array (the
> reason I am going for this
> approach is that I do not know the length of the individual strings at the
> time I construct
> the array, I only know its shape). The original strings are stored
> in a std::vector instance. The approach I took was something like
> this
>
> std::vector buffer = ;
> NpyIter *iter = NpyIter_New(numpy_array,
> NPY_ITER_READWRITE | NPY_ITER_C_INDEX |
> NPY_ITER_REFS_OK,
> NPY_CORDER , NPY_NO_CASTING,nullptr);
> if(iter==NULL)
> {
> return;
> }
> NpyIter_IterNextFunc *iternext = NpyIter_GetIterNext(iter,nullptr);
> if(iternext == NULL)
> {
> std::cerr<<"Could not instantiate next iterator function"< return;
> }
> PyObject **dataptr = (PyObject**)NpyIter_GetDataPtrArray(iter);
> for(auto string: buffer)
> {
> dataptr[0] = PyString_FromSting(string); // this string construction
> seem to work
> iternext(iter);
> }
> NpyIter_Deallocate(iter);
>
>
> This code snippet is a bit stripped down with all the safety checks
> removed to make
> things more readable.
> However, the array I get back still contains only a None instance. Does
> anyone have an idea
> what I am doing wrong here?
> Thanks in advance.
>
> best regards
>Eugen
>
>
Honestly, given that you're iterating over a single 1D array you've just
constructed, I don't think I would even bother trying to use the iterator.
For this case, a simple loop will be both concise and clear.
Eric
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Re: [Numpy-discussion] Using the C-API iterator with object arrays
On Mon, Feb 12, 2018 at 12:13 PM Eugen Wintersberger <
eugen.wintersber...@gmail.com> wrote:
> Hi there,
> I have a question concerning the numpy iterator C-API. I want to create a
> numpy
> string array using NPY_OBJECT as a datatype for creating the array (the
> reason I am going for this
> approach is that I do not know the length of the individual strings at the
> time I construct
> the array, I only know its shape). The original strings are stored
> in a std::vector instance. The approach I took was something like
> this
>
> std::vector buffer = ;
> NpyIter *iter = NpyIter_New(numpy_array,
> NPY_ITER_READWRITE | NPY_ITER_C_INDEX |
> NPY_ITER_REFS_OK,
> NPY_CORDER , NPY_NO_CASTING,nullptr);
> if(iter==NULL)
> {
> return;
> }
> NpyIter_IterNextFunc *iternext = NpyIter_GetIterNext(iter,nullptr);
> if(iternext == NULL)
> {
> std::cerr<<"Could not instantiate next iterator function"< return;
> }
> PyObject **dataptr = (PyObject**)NpyIter_GetDataPtrArray(iter);
> for(auto string: buffer)
> {
> dataptr[0] = PyString_FromSting(string); // this string construction
> seem to work
> iternext(iter);
> }
> NpyIter_Deallocate(iter);
>
>
> This code snippet is a bit stripped down with all the safety checks
> removed to make
> things more readable.
> However, the array I get back still contains only a None instance. Does
> anyone have an idea
> what I am doing wrong here?
>
I think you have the indirections wrong in dataptr?
NpyIter_GetDataPtrArray returns a char**, that hold the address of the
variable where the iterator holds the address of the first byte of the
current item being iterated.
When you write to dataptr[0] you are not writing to the array, but to where
the iterator holds the address of the first byte of the current item.
So you would have to write to dataptr[0][0], or **dataptr, to actually
affect the contents of the array. Of course, your dataptr being a PyObject**,
the compiler would probably complaint about such an assignment.
I think that if you define dataptr as a PyObject*** (yay, three star
programming !) and then assign to
**dataptr, everything will work fine. If that doesn't work, maybe try to
make dataptr a char**, and then assign to (PyObject *)(**dataptr) = ...
Jaime
> Thanks in advance.
>
> best regards
>Eugen
> ___
> NumPy-Discussion mailing list
> NumPy-Discussion@python.org
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>
--
(\__/)
( O.o)
( > <) Este es Conejo. Copia a Conejo en tu firma y ayúdale en sus planes
de dominación mundial.
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[Numpy-discussion] Using the C-API iterator with object arrays
Hi there,
I have a question concerning the numpy iterator C-API. I want to create
a numpy
string array using NPY_OBJECT as a datatype for creating the array (the
reason I am going for this
approach is that I do not know the length of the individual strings at
the time I construct
the array, I only know its shape). The original strings are stored
in a std::vector instance. The approach I took was something like
this
std::vector buffer = ;
NpyIter *iter = NpyIter_New(numpy_array,
NPY_ITER_READWRITE | NPY_ITER_C_INDEX |
NPY_ITER_REFS_OK,
NPY_CORDER , NPY_NO_CASTING,nullptr);
if(iter==NULL)
{
return;
}
NpyIter_IterNextFunc *iternext = NpyIter_GetIterNext(iter,nullptr);
if(iternext == NULL)
{
std::cerr<<"Could not instantiate next iterator function"<
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