make it generic

f.py

@@ -1,16 +1,17 @@
 # ruff: noqa
-# type: ignore
-from typing import Any
+from typing import Any, TYPE_CHECKING, TypeVar
 import pandas as pd
 import polars as pl
 
 import narwhals as nw
 
+T = TypeVar("T")
+
 
 def my_agnostic_function(
-    suppliers_native: nw.typing.T,
-    parts_native: nw.typing.T,
-) -> nw.typing.T:
+    suppliers_native: T,
+    parts_native: T,
+) -> T:
     suppliers = nw.DataFrame(suppliers_native)
     parts = nw.DataFrame(parts_native)
 

narwhals/dataframe.py

@@ -26,7 +26,7 @@
 class DataFrame(Generic[T]):
     def __init__(
         self,
-        df: Any,
+        df: T,
         *,
         is_eager: bool = False,
         is_lazy: bool = False,
@@ -35,7 +35,7 @@ def __init__(
         self._is_eager = is_eager
         self._is_lazy = is_lazy
         if implementation is not None:
-            self._dataframe = df
+            self._dataframe: Any = df
             self._implementation = implementation
             return
         if (pl := get_polars()) is not None and isinstance(

narwhals/series.py

@@ -15,14 +15,14 @@
 class Series(Generic[T]):
     def __init__(
         self,
-        series: Any,
+        series: T,
         *,
         implementation: str | None = None,
     ) -> None:
         from narwhals.pandas_like.series import PandasSeries
 
         if implementation is not None:
-            self._series = series
+            self._series: Any = series
             self._implementation = implementation
             return
         if (pl := get_polars()) is not None and isinstance(series, pl.Series):