autotest: Add a VSIFile wrapper class

[dbaston]

What does this PR do?

This PR adds a gdal.vsi_open() function that returns a file-like object, allowing virtual files to be used as "regular" Python files in some cases. For example, a zipped CSV can be read using the Python csv module:

with gdal.vsi_open(f'/vsizip/prime_meridian.csv') as f:
    records = [x for x in csv.DictReader(f)]

assert records[2]['INFORMATION_SOURCE'] == "Institut Geographique National (IGN), Paris"

Still need to correctly handle different linebreak/OS combinations, ensure errors are raised when accessing a closed file, handle append mode (or raise error), and probably other things.

What are related issues/pull requests?

Tasklist

• [ ] Add test case(s)
• [ ] Add documentation
• [ ] Updated Python API documentation (swig/include/python/docs/)
• [ ] Review
• [ ] Adjust for comments
• [ ] All CI builds and checks have passed

[coveralls]

coverage: 69.146% (-0.002%) from 69.148% when pulling 3e747a92358d86e14107f14b0ae63829e7f995ec on dbaston:python-vsifile-class into 0890073d8bfc093e1210b02022e7c694faff8cc8 on OSGeo:master.

[rcoup]

If it's helpful, here's an implementation we have been using at Koordinates for a while, with a set of tests: feel free to crib anything that's useful. I've licensed it as MIT. Any questions most welcome.

https://gist.github.com/rcoup/5f4b49149ca26084eed4dccfd1b12895

• was written quite a while ago — I would guess it could be simpler today incorporating some stdlib updates in recent Python versions and/or other bugfixes. (eg: not having open() essentially C&P)
• Inheriting from io.RawIOBase means it can fit under/into the standard python buffered & text IO wrapper classes
• I've manually removed/replaced/inlined use of a handful of internal library functions & test setup. If there's anything you get stuck on please ask.

[dbaston]

Fantastic, thank you!

[dbaston]

I have not forgotten about this. I'm leaning towards moving it to gdaltest to focus on internal use for now.

[github-actions[bot]]

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