Fix/from native update version

[camriddell]

Description

Calling from_native(nw.DataFrame(…), version=…) would always return the passed DataFrame/Series object.
This ignores the version that is specified in the version argument.

Instead, for a given narwhals DataFrame/Series from_native now returns the same object if the versions match and creates a new object if the versions do not match.

Note, 2 clean up items are also added in this PR.

Before:

import narwhals as nw, narwhals.stable.v1 as nw_v1
import polars as pl

native = pl.DataFrame({"a": [1, 2, 3]})

unstable = nw.from_native(native)
stablified = nw_v1.from_native(unstable)

print(
    isinstance(stablified, nw_v1.DataFrame), # False
    isinstance(stablified, nw.DataFrame),    # True
    sep='\n'
)

stable = nw_v1.from_native(native)
unstablified = nw.from_native(unstable)

print(
    isinstance(unstablified, nw_v1.DataFrame), # False
    isinstance(unstablified, nw.DataFrame),    # True
    sep='\n'
)

After:

import narwhals as nw, narwhals.stable.v1 as nw_v1
import polars as pl

native = pl.DataFrame({"a": [1, 2, 3]})

unstable = nw.from_native(native)
stablified = nw_v1.from_native(unstable)

print(
    isinstance(stablified, nw_v1.DataFrame), # True
    isinstance(stablified, nw.DataFrame),    # True (since nw.v1.DataFrame is subclass of nw.DataFrame)
    sep='\n'
)

stable = nw_v1.from_native(native)
unstablified = nw.from_native(unstable)

print(
    isinstance(unstablified, nw_v1.DataFrame), # False
    isinstance(unstablified, nw.DataFrame),    # True
    sep='\n'
)

reported by hoxbro (Holoviews) on Discord #help channel

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

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

Related issues

• Related issue #<issue number>
• Closes #<issue number>

Checklist

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

[camriddell]

Hoping this has been an oversight and wasn't excluded for a strong reason. This change makes the DataFrame/LazyFrame api a bit more consistent internally.

[dangotbanned]

Yeah nice one, thanks @camriddell!

If you dig through the blame (I think) I added these on Series & DataFrame at the same time as the from_* constructors.

LazyFrame didn't get any new methods, so it slipped through 😅

[camriddell]

@MarcoGorelli I believe the nightly failure isn't due to this change but perhaps something that needs to be accounted for in pandas. Shall I open up an Issue with this? Or do you believe it is relevant to this PR?

[dangotbanned]

IIRC, there may be a comment somewhere mentioning the error?

(Ignore me if this is too vague 😂)

[dangotbanned]

@camriddell I should probably check what was mentioned on discord - but from reading the PR I'm a bit confused on the problem that's being solved.

(#3515 (comment)) is all good - but something seems strange to me that calling from_native changes the version 🤔

FWIW, I don't think from_native should accept narwhals-level objects, but we are where we are 😅