Feat/add collect schema to interchange dfs (#1646)

narwhals/_duckdb/dataframe.py

@@ -151,3 +151,11 @@ def _change_version(self: Self, version: Version) -> Self:
 
     def _from_native_frame(self: Self, df: Any) -> Self:
         return self.__class__(df, version=self._version)
+
+    def collect_schema(self) -> dict[str, DType]:
+        return {
+            column_name: native_to_narwhals_dtype(str(duckdb_dtype), self._version)
+            for column_name, duckdb_dtype in zip(
+                self._native_frame.columns, self._native_frame.types
+            )
+        }

narwhals/_ibis/dataframe.py

@@ -129,3 +129,9 @@ def _change_version(self: Self, version: Version) -> Self:
 
     def _from_native_frame(self: Self, df: Any) -> Self:
         return self.__class__(df, version=self._version)
+
+    def collect_schema(self) -> dict[str, DType]:
+        return {
+            column_name: native_to_narwhals_dtype(ibis_dtype, self._version)
+            for column_name, ibis_dtype in self._native_frame.schema().items()
+        }

tests/frame/interchange_schema_test.py

@@ -156,6 +156,7 @@ def test_interchange_schema_ibis(
     assert result == expected
     assert df["a"].dtype == nw.Int64
     assert df.columns == list(expected.keys())
+    assert df.collect_schema() == expected
 
 
 def test_interchange_schema_duckdb() -> None:
@@ -221,6 +222,7 @@ def test_interchange_schema_duckdb() -> None:
     assert result == expected
     assert df["a"].dtype == nw.Int64
     assert df.columns == list(expected.keys())
+    assert df.collect_schema() == expected
 
 
 def test_invalid() -> None: