Open mfdataset enchancement

[pratiman-91]

• Closes better handling of invalid files in open_mfdataset #6736
• User visible changes (including notable bug fixes) are documented in whats-new.rst

Added new argument in open_mfdataset to better handle the invalid files.

errors : {'ignore', 'raise', 'warn'}, default 'raise'
        - If 'raise', then invalid dataset will raise an exception.
        - If 'ignore', then invalid dataset will be ignored.
        - If 'warn', then a warning will be issued for each invalid dataset.

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[max-sixty]

I'm not the expert, but this looks reasonable! Any other thoughts?

Assuming no one thinks it's a bad idea, we would need tests.

[headtr1ck]

I think it is a good idea.

But the way it is implemented here seems overly complicated and repetitive.
I would suggest to revert the logic: first build up the list wrapped in a single try and then handle the three cases in the except block.

[headtr1ck]

This is never being raised because it is catched by the outer try-except.

Also, to keep the complexity lower, check this before entering the if else block: if errors not in ("raise", "warn", "ignore"): raise ValueError(...)

[pratiman-91]

Thanks @headtr1ck for pointing this out. I have made changes to the logic based on your suggestions.