Crash when reaching warnings.DeprecationWarning

[ameraner]

Describe the bug
After #1565 , Satpy crashes when reaching e.g.
https://github.com/pytroll/satpy/blob/master/satpy/scene.py#L273-L274

To Reproduce

new_scn = scn.resample(scn.min_area())

Expected behavior
Show the DeprecationWarning and don't crash.
This is solved by removing the warnings.

warnings.warn("'min_area' is deprecated, use 'coarsest_area' instead.",
                      DeprecationWarning)

Actual results

  File "/tcenas/home/andream/code/satpy_latest/satpy/satpy/scene.py", line 274, in min_area
    warnings.DeprecationWarning)
AttributeError: module 'warnings' has no attribute 'DeprecationWarning'

Environment Info:
Python 3.7, latest Satpy master after the mentioned PR

[ameraner]

@pnuu @djhoese @mraspaud FYI

[ameraner]

Are those warnings being suppressed anyway somewhere? Not sure how, but they don't show up for me.

[djhoese]

This is the main discussion about #1554. DeprecationWarning warnings are not shown by Python by default. So a lot of Satpy deprecation warnings (and other scientific libraries) choose to use the default UserWarning. UserWarnings do show up by default. However, as @gerritholl pointed out you can't handle deprecation warnings in a special way if they are indistinguishable from all the other UserWarnings. #1554 is the best compromise we could come up with.

[djhoese]

@ameraner If you haven't already can you make a PR for the fix you mentioned above?

[ameraner]

Done!