feat(python): additional autocomplete affordances for IPython users

[alexander-beedie]

Closes #5468.

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Implements special _ipython_key_completions_ method, enabling autocomplete suggestions in IPython for polars DataFrame columns and Series.struct fields:

[ritchie46]

That's really nice. Would this be possible for pl.col(".. as well?

EDIT:

I don't think so, it is hard to know the context we use statically.

[alexander-beedie]

it is hard to know the context we use statically.

Exactly - the col object is isolated from the frame context it'll be used in (and the magic method only applies to dict-style __getitem__ lookup, eg: obj['<str>...). Was looking for other opportunities to deploy it - at least I found struct, heh.

• ref: Integrating your objects with IPython