Add access point to global_attrs to netCDF4FileHandler

[tsukada-cs]

In the NetCDF4FileHandler, it can't get all global_attributes in NetCDF with a single command.
I think NetCDF4FileHandler should have a method to get all global_attributes at once without the attribute’s name.

In this PR, we can access all global_attributes with

wrapper['/attr'] or wrapper['/attrs']

• Tests added
• Fully documented

[mraspaud]

This looks good to me, just a linting error to fix so far :)

[codecov]

Codecov Report

Merging #1772 (0dcfd46) into main (4d34625) will increase coverage by 0.08%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1772      +/-   ##
==========================================
+ Coverage   92.82%   92.91%   +0.08%     
==========================================
  Files         263      265       +2     
  Lines       38717    39037     +320     
==========================================
+ Hits        35940    36272     +332     
+ Misses       2777     2765      -12     

Flag	Coverage Δ
behaviourtests	4.76% <0.00%> (-0.04%)	⬇️
unittests	93.45% <100.00%> (+0.08%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
satpy/readers/netcdf_utils.py	100.00% <100.00%> (ø)
satpy/tests/reader_tests/test_netcdf_utils.py	94.89% <100.00%> (+0.10%)	⬆️
satpy/readers/abi_l1b.py	95.83% <0.00%> (-0.89%)	⬇️
satpy/scene.py	92.32% <0.00%> (ø)
satpy/_config.py	98.59% <0.00%> (ø)
satpy/demo/__init__.py	100.00% <0.00%> (ø)
satpy/demo/viirs_sdr.py	100.00% <0.00%> (ø)
satpy/readers/abi_base.py	94.59% <0.00%> (ø)
satpy/tests/reader_tests/test_clavrx.py	100.00% <0.00%> (ø)
satpy/tests/reader_tests/test_abi_l1b.py	100.00% <0.00%> (ø)
... and 18 more

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[coveralls]

Coverage increased (+0.04%) to 93.398% when pulling 0dcfd46 on tsukada-cs:feature-add_access_point_to_global_attrs_to_NetCDF4FileHandler into 07a87af on pytroll:main.

[mraspaud]

Ok, I think these are my last comments, after that it should be good to merge :)

[tsukada-cs]

Thanks a lot!

[mraspaud]

LGTM

[djhoese]

Nice work! One more consideration: what do you think about storing the global attributes in a separate dictionary (ex. self._global_attrs = {}) or as a separate key (ex. self.file_content['/attrs'] = {}) and have that filled in in the _collect_attrs method when the file is read. We're already storing all the global attributes in self.file_content so having another copy wouldn't be that bad. You could have a special _collect_global_attrs method to do it maybe. Just a thought.

[tsukada-cs]

That's also nice idea! But I'd like to see what's going on with the current implementation. Thank you :)

[djhoese]

But I'd like to see what's going on with the current implementation.

I'm not sure I understand what you mean. Are you saying you like the current implementation and don't want to change it?

[tsukada-cs]

@djhoese Sorry for the confusion. I don't really have time for this. If someone wants to change the implementation, that's fine.

[djhoese]

@mraspaud I'm working on refactoring this and I'd like to remove the ability to use /attr and /attrs and instead make it only /attrs. Are you and @tsukada-cs ok with that?

Additional question: Should the globals dictionary have attribute keys with /attr/ prefixes? Or just the straight key?

self["/attrs"]["some_key"]
# versus
self["/attrs"]["/attr/some_key"]

[tsukada-cs]

@djhoese

Are you and @tsukada-cs ok with that?

Thank you. There is no problem with that.

I prefer

self["/attrs"]["some_key"]

, but I have no strong preference or reason for it.

[mraspaud]

Sounds good. I agree that self["/attrs"]["some_key"] looks better.

[djhoese]

Ok this is ready for re-review. Global attributes are available as handle["/attrs"] and the keys in that dictionary are just the name of the attribute. I also refactored some of the other code to hopefully clean it up a bit (smaller methods, less redundant code).

[mraspaud]

LGTM, it's nice with the simplification of the interface