Do not call warnings.simplefilter in library code

[vnmabus]

What is the bug?

In https://github.com/OSGeo/gdal/blob/master/swig/python/osgeo/__init__.py warnings.simplefilter is called to always display deprecation warnings. This changes the global warnings configuration, which is bad to do inside a library.

In our case, this happened when using an older Python version and the newest GDAL that still supported it (which triggers a message saying that newer GDAL versions will drop support for that Python version). Due to the warnings.simplefilter change, a lot of deprecation warnings from other modules flooded our logs.

We are going to patch our GDAL version suppressing calls to warnings.simplefilter. However, as this is still happening in master I wanted to open an issue for it to be fixed in the future.

Steps to reproduce the issue

Just execute the newest GDAL which still has support for an older Python version.

Versions and provenance

GDAL 3.2.3 and Python 2.7 (but it will happen again when you drop support for another Python version).

Additional context

No response

[rouault]

@idanmiara Any thought about that? I see you added that in 339a600

[idanmiara]

I frankly don't remember why I set simplefilter('always', DeprecationWarning) there, but as @vnmabus suggests it also makes sense to me to remove both calls to simplefilter.

[rouault]

thanks, will be fixed per #11141