I've just come back to this after a while and decided to try fixing (#1928 (comment))

Without adding any new @overloads, I got 5/6 passing:

I think the general issue with from_native has been that these @overloads are both strict and incomplete.
Most of them are dedicated to pass_through: Literal[True], but would have the same behavior for pass_through: bool.

Important

Simply changing one/two quickly snowballs into other issues

Suggestion

We should replace some of the parametric testing in tests/translate/from_native_test.py with something a typechecker can help us with.

Example

This test produces a # type: ignore[call-overload] in all 4 cases, but only 1 actually raises at runtime

narwhals/tests/translate/from_native_test.py

Lines 438 to 460 in aef26ce

    
           @pytest.mark.parametrize( 
        
               ("eager_only", "pass_through", "context"), 
        
               [ 
        
                   (False, False, does_not_raise()), 
        
                   (False, True, does_not_raise()), 
        
                   (True, True, does_not_raise()), 
        
                   (True, False, pytest.raises(TypeError, match="Cannot only use")), 
        
               ], 
        
           ) 
        
           def test_eager_only_pass_through_main( 
        
               constructor: Constructor, *, eager_only: bool, pass_through: bool, context: Any 
        
           ) -> None: 
        
               if not any(s in str(constructor) for s in ("pyspark", "dask", "ibis", "duckdb")): 
        
                   pytest.skip(reason="Non lazy or polars") 
        
               df = constructor(data) 
        
               with context: 
        
                   res = nw.from_native(df, eager_only=eager_only, pass_through=pass_through)  # type: ignore[call-overload] 
        
                   if eager_only and pass_through: 
        
                       assert not isinstance(res, nw.LazyFrame) 
        
                   else: 
        
                       assert isinstance(res, nw.LazyFrame)

With the changes I made for Series overloads, I then went back and isolated the failing case (it started giving a different warning, which prompted this):

def test_eager_only_pass_through_main(constructor: Constructor) -> None:
    if not any(s in str(constructor) for s in ("pyspark", "dask", "ibis", "duckdb")):
        pytest.skip(reason="Non lazy or polars")

    df = constructor(data)

    r1 = nw.from_native(df, eager_only=False, pass_through=False)
    r2 = nw.from_native(df, eager_only=False, pass_through=True)
    r3 = nw.from_native(df, eager_only=True, pass_through=True)

    assert isinstance(r1, nw.LazyFrame)
    assert isinstance(r2, nw.LazyFrame)
    assert not isinstance(r3, nw.LazyFrame)

    with pytest.raises(TypeError, match=r"Cannot.+use.+eager_only"):
        nw.from_native(df, eager_only=True, pass_through=False)  # type: ignore[type-var]

	@pytest.mark.parametrize(
	("eager_only", "pass_through", "context"),
	[
	(False, False, does_not_raise()),
	(False, True, does_not_raise()),
	(True, True, does_not_raise()),
	(True, False, pytest.raises(TypeError, match="Cannot only use")),
	],
	)
	def test_eager_only_pass_through_main(
	constructor: Constructor, *, eager_only: bool, pass_through: bool, context: Any
	) -> None:
	if not any(s in str(constructor) for s in ("pyspark", "dask", "ibis", "duckdb")):
	pytest.skip(reason="Non lazy or polars")

	df = constructor(data)

	with context:
	res = nw.from_native(df, eager_only=eager_only, pass_through=pass_through) # type: ignore[call-overload]
	if eager_only and pass_through:
	assert not isinstance(res, nw.LazyFrame)
	else:
	assert isinstance(res, nw.LazyFrame)

missing overload for nw.from_native(obj, eager_only=True, series_only=True) #1928

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missing overload for `nw.from_native(obj, eager_only=True, series_only=True)` #1928