[Enh]: Add shortened aliases for supported __dunder__ methods on expr

[CangyuanLi]

What type of PR is this? (check all applicable)

• 💾 Refactor
• ✨ Feature
• 🐛 Bug Fix
• 🔧 Optimization
• 📝 Documentation
• ✅ Test
• 🐳 Other

Related issues

• Related issue Support operator aliases in Expr #2213
• Closes #<issue number>

Checklist

• Code follows style guide (ruff)
• Tests added
• Documented the changes

If you have comments or can explain your changes, please do so below

This PR adds shortened aliases (e.g. sub, lt) for supported binary operators (e.g. sub, lt), mimicing the Polars API. This makes method chaining much more convenient.

[CangyuanLi]

Hi all, thanks for bearing with me on my first PR! Pre-commit is failing because there are methods on Expr that are not on Series. What is narwhal's policy on breaking from the polars API? In polars, these methods are only implemented on Expr, not Series.

[FBruzzesi]

Hi all, thanks for bearing with me on my first PR!

Hey @CangyuanLi thanks for taking the initiative 🙏🏼

Pre-commit is failing because there are methods on Expr that are not on Series. What is narwhal's policy on breaking from the polars API? In polars, these methods are only implemented on Expr, not Series.

You can add these methods in

narwhals/utils/check_api_reference.py

Line 63 in f99778e

EXPR_ONLY_METHODS = {"over", "map_batches"}

so that the check should pass

[MarcoGorelli]

thanks for your pr! sorry, I forgot to reply to the issue

tbh I'm not totally sure about these. You can already type out __sub__ / etc. if you want to chain the operations, i'm not sure about expanding the api with these

on the other hand, these are nice to have documented, whereas it's a bit awkward to document the __ methods (and I think most users wouldn't know what they do)

i'll think about this a little more

[CangyuanLi]

Thank you! I agree that its more of a nice-to-have. My argument in favor would be that it makes reasoning about the order of operations much faster (at least for me). Calling the dunder methods does that as well but does introduce visual clutter.