Feature: added properties to VortexScanner (#5500)

added property to VortexScanner

fixes #5454

```
import vortex as vx

vx.io.write(vx.array([{"col1": "a string"}]), 'foo.vortex')
x = vx.open('foo.vortex').to_dataset().scanner().projected_schema
```

Signed-off-by: Siddharth Kumar <[email protected]>
Co-authored-by: Connor Tsui <[email protected]>

Author: sherlockbeard

vortex-python/python/vortex/dataset.py

@@ -791,6 +791,22 @@ def __init__(
     def schema(self):
         return self._dataset.schema
 
+    @property
+    @override
+    def dataset_schema(self) -> pyarrow.Schema:
+        return self._dataset.schema
+
+    @property
+    @override
+    def projected_schema(self) -> pyarrow.Schema:
+        if self._columns:
+            fields: list[pa.Field[pa.DataType]] = [
+                self._dataset.schema.field(c)  # pyright: ignore[reportUnknownMemberType]
+                for c in self._columns
+            ]
+            return pyarrow.schema(fields)
+        return self._dataset.schema
+
     @override
     def count_rows(self):
         return self._dataset.count_rows(

vortex-python/test/test_scan.py

@@ -64,3 +64,13 @@ def test_scan_with_cast(vxfile: vx.VortexFile):
         [{"index": 1, "string": pa.scalar("1", pa.string_view()), "bool": False, "float": math.sqrt(1)}]
     )
     assert str(actual.to_arrow_array()) == str(expected)
+
+
+def test_scanner_property_projected(vxfile: vx.VortexFile):
+    assert vxfile.to_dataset().scanner(columns=["bool"]).projected_schema == pa.schema([("bool", pa.bool_())])
+
+
+def test_scanner_property_dataset_schema(vxfile: vx.VortexFile):
+    assert vxfile.to_dataset().scanner().dataset_schema == pa.schema(
+        [("bool", pa.bool_()), ("float", pa.float64()), ("index", pa.int64()), ("string", pa.string_view())]
+    )