[gdal-dev] pass gdal dataset as an argument from Python to C

[Sean Gillies]

I believe it's possible, yes, but it will be challenging. I'm not aware of
anybody else doing this.

In
https://github.com/OSGeo/gdal/blob/trunk/gdal/swig/python/extensions/gdal_wrap.cpp
you can see examples of C++ functions that access the GDAL objects
referenced by Python objects. This isn't a stable public API by any means,
and therefore I hesitate to recommend it. Maybe Even would be able to
comment more on how much support there is for the SWIG-generated C++ Python
classes.

I presume you've already tried writing "_my_module" in Python and found it
to be too slow?

Good luck!

On Mon, Nov 27, 2017 at 9:34 AM, Shawn Gong <SGONG at mdacorporation.com>
wrote:

> Thank you Sean.
>
>
>
> What I want to do is to compile C/C++ code into "_my_c_module.pyd" and
> then to be called by Python. The Python code passes an argument to C/C++.
>
> I did previously by passing a file name (str) or a numpy array as
> argument to C/C++, and it is all good.
>
> This time I want to pass a gdal dataset as an argument:
>
>
>
> in Python:
>
>     from osgeo import gdal
>
>     import _my_c_module
>
>     ds=gdal.Open('my_filename")
>
>     result = _my_c_module.function1(ds)
>
>
>
> is this possible? If yes, how?
>
>
>
>
> Shawn
> ------------------------------
> *From:* Sean Gillies [sean at mapbox.com]
> *Sent:* November-27-17 11:09 AM
> *To:* Shawn Gong
> *Cc:* gdal-dev at lists.osgeo.org
> *Subject:* Re: [gdal-dev] pass gdal dataset as an argument from Python to
> C
>
> Shawn,
>
> PyObject and GDALDatasetH are incompatible types and you can't pass the
> former to a function that expects the latter. I'm surprised your program
> can compile with these incompatible types.
>
> Do you mean for your module to extend GDAL's Python bindings? If you look
> inside the C code of GDAL's Python bindings you may be able to see how to
> get the GDALDatasetH associated with a Python dataset object.
>
> Hope this helps,
>
>
> On Thu, Nov 23, 2017 at 1:25 PM, Shawn Gong <SGONG at mdacorporation.com>
> wrote:
>
>> Hi list,
>>
>>
>>
>> Has anyone done this before?
>>
>> I try to pass a gdal dataset as an argument from Python to C.
>>
>>
>>
>> in my C code, I have
>>
>> PyObject* py_my_func(PyObject *self, PyObject *args)
>> {
>>
>>     PyObject *poDataset;
>>
>>
>>
>>    if(!PyArg_ParseTuple(args, "Odd", &poDataset, &a1, &a2))
>>   {
>>     return NULL;
>>   }
>>
>>
>>
>>   my_func(poDataset, a1, a2);
>> }
>>
>>
>>
>> void my_func(GDALDatasetH hDataset, double a1, double a2)
>>
>> {
>>
>> }
>>
>>
>>
>> Python crashed and hDataset was NULL
>>
>> Is it possible to do or I did something wrong?
>>
>>
>>
>> BTW, I have passed either a filename or a gdal array as an argument from
>> Python to C, with success.
>>
>> Thanks,
>> Shawn
>>
>> _______________________________________________
>> gdal-dev mailing list
>> gdal-dev at lists.osgeo.org
>> https://lists.osgeo.org/mailman/listinfo/gdal-dev
>>
>
>
>
> --
> Sean Gillies
>



-- 
Sean Gillies
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/gdal-dev/attachments/20171127/9489576f/attachment.html>