Create pl.lit from a Python set object?

[cmdlineluser]

Description

This came up when using list.set_intersection where trying to pass a set raises a TypeError.

other = {'a', 'c'}
pl.select(pl.lit(['a', 'b', 'c']).list.set_intersection(other))

# TypeError: cannot create expression literal for value of type set: {'a', 'c'}

The caller must explictly convert it to a list/tuple, which feels a little awkward.

pl.select(pl.lit(['a', 'b', 'c']).list.set_intersection(list(other)))

# shape: (1, 1)
# ┌────────────┐
# │ literal    │
# │ ---        │
# │ list[str]  │
# ╞════════════╡
# │ ["a", "c"] │
# └────────────┘

Should Polars allow this and just treat it as if it were a list?

[alexander-beedie]

... better to leave it up to the caller to decide if unstable sort order is acceptable for their usage

Actually, re-reading the example... the set is being provided to set_intersection, it isn't the root expression. Hmm... Let me think about that - it may not be so unreasonable that way round, though I believe there will still be element-order instability in some of the other set-function results, which I don't think we want in what are still list-namespace ops (and special-casing this method over the others would feel a bit inconsistent 🤔). Need to check what we're currently doing here in terms of stability.

[ritchie46]

I don't think we should. It are set operations done on "lists", not on "sets". Polars doesn't have a set type and making an exception for 1 expression is not something the IR should deal with.