[gdal-dev] Python bindings: enabling exceptions by default?

[Frank Warmerdam]

Folks,

As long as there is a clear path to disabling python exception handling
fairly cleanly I can live with it.  Like Kurt, we have a large code base
using GDAL mostly without exceptions enabled for GDAL.

If there is going to be a change, I also agree 4.0 is the time to do it.

Best regards,
Frank


On Mon, Mar 20, 2023 at 4:07 PM Kurt Schwehr <schwehr at gmail.com> wrote:

> We are heavy users of the swig bindings. We have some Fiona users and are
> only just now in the process of starting to use rasterio. We have only 3
> instances of calling UseExceptions. Turning on UseExceptions
> immediately blew up a bunch of my tests that were making incorrect
> assumptions. Nothing major, but I haven't looked for more than a couple
> seconds for trouble.
>
> +1 for switching to have it enabled by default. I'm not sure if it would
> be better with 3.7.0 or 4.0.0.
>
> On Mon, Mar 20, 2023 at 10:58 AM Howard Butler <howard at hobu.co> wrote:
>
>>
>>
>> > On Mar 19, 2023, at 7:34 AM, Even Rouault <even.rouault at spatialys.com>
>> wrote:
>> >
>> > Hi,
>> >
>> > I've prepared a pull request that does the above, but this raises a
>> number of questions. See my longish comment at
>> https://github.com/OSGeo/gdal/pull/7475#issuecomment-1475239852.
>> Thoughts appreciated
>>
>> First off, thank you for doing this.
>>
>> Speaking for myself, pretty much all of the ogr.py/gdal.py code I've
>> written for the past 15 years has gdal.UseExceptions() after the "from
>> osgeo import gdal" import. The reasons why we had to have this 15 years ago
>> were reasonable, but now it is just confusing boilerplate. It's time to
>> ditch it.
>>
>> It has been a regret that we didn't clean up the secondary effects of
>> UseExceptions/DontUseExceptions a long time ago. I'm sure the original sin
>> was a result of my mucking with the SWIG bindings to get something that
>> kind of worked and giving up after that. I'm glad your PR addresses this
>> and makes things better for other handler-aware code that is often mixed
>> together with gdal.py such as Fiona/rasterio, QGIS bindings, or PDAL stuff
>> (in my case).
>>
>> As for enabling them by default at our next 3.7 release ... one one hand,
>> it has been fifteen years already and the project has been telegraphing
>> through the options that this could/should change. On the other, GDAL is
>> *very* conservative with API evolution, and making UseExceptions default
>> behavior in the Python bindings breaks existing code that wasn't doing
>> gdal.UseExceptions already. The nice thing about activating this behavior
>> is that it causes it to throw an exception and tell the user about
>> something that was otherwise silently failing, so the remedy in the case of
>> most of these breakages is going to be clear.
>>
>> I would vote that we go for enabling UseExceptions by default for GDAL
>> 3.7 based on the following assumptions:
>> * The group that will feel the largest impact by the change is GDAL's own
>> autotest suite
>> * Exceptions are the Python Way, and default behavior of GDAL's bindings
>> is out of step
>> * Tons of user-land code is already doing UseExceptions, as it is a
>> practice that is recommended in many tutorials and books and SE posts
>> * The largest portion of GDAL-using Python developers are using Rasterio
>> or Fiona, not gdal.py and ogr.py, and they would not be impacted by these
>> changes (and maybe be impacted positively as the ticket describes).
>>
>> Are you a GDAL Python bindings user? Would you be impacted by this policy
>> change? Please chime in.
>>
>> Howard
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>>
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-- 
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I set the clouds in motion - turn up   | Frank Warmerdam,
warmerdam at pobox.com
light and sound - activate the windows | +1 650-701-7823
and watch the world go round - Rush    | Geospatial Software Developer
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