Ensure file handlers all use filenames as strings

[honnorat]

All subclasses of BaseFileHandler have been reviewed to be sure that their constructor Subclass.__init__ uses BaseFileHandler.filename instead of the constructor argument.

BaseFileHandler.filename is forced to be a string. The result is that pathlib.Path or strings can be used equally for building an instance of any subclass.

• Closes Review subclasses of BaseFileHander #453
• Tests added
• Tests passed
• Passes git diff origin/master '**/*py' | flake8 --diff

[djhoese]

Why didn't you force str(filename) when the base reader class creates the file handlers like I mentioned in #453?

[honnorat]

What do you mean by "the base reader class" ?

[djhoese]

Sorry I was trying to catch a bus and had to type fast 😜

I meant FileYAMLReader the "reader" class that creates the individual "file handler" classes. If you changed this line I think it would do the equivalent: https://github.com/pytroll/satpy/blob/master/satpy/readers/yaml_reader.py#L396

[coveralls]

Coverage increased (+0.01%) to 72.99% when pulling 8cb66eb on EXWEXs:fix-basefilehandler into 38fb064 on pytroll:master.

[codecov]

Codecov Report

Merging #455 into master will increase coverage by 0.01%.
The diff coverage is 56.66%.

@@            Coverage Diff             @@
##           master     #455      +/-   ##
==========================================
+ Coverage   72.97%   72.98%   +0.01%     
==========================================
  Files         134      134              
  Lines       17695    17686       -9     
==========================================
- Hits        12913    12909       -4     
+ Misses       4782     4777       -5

Impacted Files	Coverage Δ
satpy/readers/safe_sar_c.py	20.1% <ø> (+0.1%)	⬆️
satpy/readers/native_msg.py	15.02% <ø> (+0.07%)	⬆️
satpy/readers/iasi_l2.py	98.78% <ø> (-0.02%)	⬇️
satpy/readers/hdf4_caliopv3.py	31.57% <ø> (+0.54%)	⬆️
satpy/tests/test_yaml_reader.py	98.64% <ø> (-0.02%)	⬇️
satpy/readers/hdfeos_l1b.py	14.71% <0%> (ø)	⬆️
satpy/readers/li_l2.py	23.88% <0%> (+0.35%)	⬆️
satpy/readers/maia.py	19.27% <0%> (ø)	⬆️
satpy/readers/fci_fdhsi.py	20.22% <0%> (+0.22%)	⬆️
satpy/readers/nc_nwcsaf.py	17.02% <0%> (ø)	⬆️
... and 9 more

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[honnorat]

I see your point. The advantage of this PR is that the changes it proposes are independent of the complex machinery in satpy.readers.yaml_readers. It ensures that when you use the FileHandlers, you are sure that MyFileHandler.filename is a string, whatever the way it was created.

All changes in the subclasses only make this use uniform across the entire code base.

Your solution is good enough for today, though.