depr(python): Deprecate DataType.is_nested

[stinodego]

I really like the idea of extending our DataType class with methods like is_nested() and is_integer() (and other groups). But these should not be properties - they should be (class)methods just like we have Series.is_integer() and DataFrame.is_empty() etc.

Unfortunately, is_nested is some sort of custom property, which means we have to break it before we can implement DataType.is_nested() as a classmethod.

Changes

• Add the NESTED_DTYPES group
• Deprecate DataType.is_nested, suggest using dtype in pl.NESTED_DTYPES instead (until we implement DataType.is_nested() as a breaking change).

@alexander-beedie Any thoughts?

[alexander-beedie]

The changes here all make sense to me, though I'm not quite as convinced about having a method per-dtype (in the future). Though maybe it's just... extremely clear? 🤔

Could also have a series of more generic methods so we don't have to update the class every time we add a new dtype (which isn't going to be often, but still... Thinking out loud, something along these lines might also work?

General match, eg: "Datetime == Datetime("us")
Exact match, eg: "Datetime("us") == Datetime("us"):

• dtype.is_( ..., exact=True/False )
• dtype.is_not( ..., exact=True/False )

Matches one of the given types:

• dtype.in_( ..., exact=True/False )
• dtype.not_in( ..., exact=True/False )

Need to see a few proposed usage examples to make better sense of it; perhaps we want to have dtype-specific and generic methods?

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This also reminds me that I still need to get around to adding support for wildcard selection of nested/compound types in col (for selectors) 😅

[stinodego]

I was planning on opening an issue explaining my intentions here, will do so shortly! Then we can take some time to discuss before I dive in 😄

Whichever way we go, though, I think we need to get rid of the custom is_struct property ASAP as I believe it should have been a classmethod in the first place and it cannot neatly be replaced without being a breaking change.

[alexander-beedie]

Whichever way we go, though, I think we need to get rid of the custom is_struct property ASAP as I believe it should have been a classmethod in the first place and it cannot neatly be replaced without being a breaking change.

Agreed! :)