add SOLRAD data parser to iotools

[wholmgren]

https://www.esrl.noaa.gov/gmd/grad/solrad/index.html

• Closes issue #xxxx
• I am familiar with the contributing guidelines.
• Fully tested. Added and/or modified tests to ensure correct behavior for all reasonable inputs. Tests (usually) must pass on the TravisCI and Appveyor testing services.
• Updates entries to docs/sphinx/source/api.rst for API changes.
• Adds description and name entries in the appropriate docs/sphinx/source/whatsnew file for all changes.
• Code quality and style is sufficient. Passes LGTM and SticklerCI checks.
• New code is fully documented. Includes sphinx/numpydoc compliant docstrings and comments in the code where necessary.
• Pull request is nearly complete and ready for detailed review.

Needs tests.

[cwhanse]

should be testfile = os.path.join(test_dir, 'data', '703165TY.csv') for cross-platform compatibility

[wholmgren]

The path you've specified would be pvlib/test/data/703165TY.csv, but the data is in pvlib/data/abq19056.dat. I am pretty sure that os.path handles the .. specification as needed for the platform. The appveyor builds do not object to this pattern.

[cwhanse]

Of course. I substituted a file I have to test. Doesn't work on Windows. C:\python\pvlib-dev\pvlib-python\pvlib\../data/abq19056.dat

[wholmgren]

Hm... Appveyor tests run on Windows so I am quite confused.

[cwhanse]

Hmmm... the string is interpreted correctly when a file operation is performed, so it's OK as coded. I still think my suggestion is an improvement.

import os
import inspect

test_dir = os.path.dirname(
    os.path.abspath(inspect.getfile(inspect.currentframe())))

print(test_dir)

testfile = os.path.join(test_dir, '../data/703165TY.csv')
print(testfile)

with open(testfile) as infile:
    r = infile.readline()
    print(r)

produces

C:\python\pvlib-dev\pvlib-python\pvlib\test
C:\python\pvlib-dev\pvlib-python\pvlib\test\../data/703165TY.csv
703165,"SAND POINT",AK,-9.0,55.317,-160.517,7

[wholmgren]

Is '..' acceptable? testfile = os.path.join(test_dir, '..', 'data', '703165TY.csv')

[wholmgren]

I see it's called pardir: https://docs.python.org/3/library/os.html#os.pardir

[cwhanse]

that would maintain the OS-specific separator so the string doesn't have a mix of \ and /

[cwhanse]

or use os.pardir to avoid the ..

[wholmgren]

Thanks. I thought os.path.join was smarter than it was because the tests have never complained about that pattern in the past. Looking forward to the Python 3 only days and using pathlib.

[cwhanse]

see above comment

[wholmgren]

some examples from the NOAA ftp realtime folder: