Add requested_schema argument to PyCapsule interface

tools/pythonpkg/duckdb-stubs/__init__.pyi

@@ -412,7 +412,7 @@ class DuckDBPyRelation:
     def list(self, column: str, groups: str = ..., window_spec: str = ..., projected_columns: str = ...) -> DuckDBPyRelation: ...
 
     def arrow(self, batch_size: int = ...) -> pyarrow.lib.Table: ...
-    def __arrow_c_stream__(self) -> object: ...
+    def __arrow_c_stream__(self, requested_schema: Optional[object] = None) -> object: ...
     def create(self, table_name: str) -> None: ...
     def create_view(self, view_name: str, replace: bool = ...) -> DuckDBPyRelation: ...
     def describe(self) -> DuckDBPyRelation: ...

tools/pythonpkg/src/include/duckdb_python/pyrelation.hpp

@@ -194,7 +194,7 @@ struct DuckDBPyRelation {
 
 	PolarsDataFrame ToPolars(idx_t batch_size);
 
-	py::object ToArrowCapsule();
+	py::object ToArrowCapsule(const py::object &requested_schema = py::none());
 
 	duckdb::pyarrow::RecordBatchReader ToRecordBatch(idx_t batch_size);
 

tools/pythonpkg/src/pyrelation.cpp

@@ -946,7 +946,7 @@ duckdb::pyarrow::Table DuckDBPyRelation::ToArrowTable(idx_t batch_size) {
 	return ToArrowTableInternal(batch_size, false);
 }
 
-py::object DuckDBPyRelation::ToArrowCapsule() {
+py::object DuckDBPyRelation::ToArrowCapsule(const py::object &requested_schema) {
 	if (!result) {
 		if (!rel) {
 			return py::none();

tools/pythonpkg/src/pyrelation/initialize.cpp

@@ -73,7 +73,8 @@ static void InitializeConsumers(py::class_<DuckDBPyRelation> &m) {
 
 			https://arrow.apache.org/docs/dev/format/CDataInterface/PyCapsuleInterface.html
 		)";
-	m.def("__arrow_c_stream__", &DuckDBPyRelation::ToArrowCapsule, capsule_docs);
+	m.def("__arrow_c_stream__", &DuckDBPyRelation::ToArrowCapsule, capsule_docs,
+	      py::arg("requested_schema") = py::none());
 	m.def("record_batch", &DuckDBPyRelation::ToRecordBatch,
 	      "Execute and return an Arrow Record Batch Reader that yields all rows", py::arg("batch_size") = 1000000)
 	    .def("fetch_arrow_reader", &DuckDBPyRelation::ToRecordBatch,

tools/pythonpkg/tests/fast/arrow/test_arrow_pycapsule.py

@@ -21,9 +21,9 @@ def __init__(self, obj):
                 self.obj = obj
                 self.count = 0
 
-            def __arrow_c_stream__(self):
+            def __arrow_c_stream__(self, requested_schema=None):
                 self.count += 1
-                return self.obj.__arrow_c_stream__()
+                return self.obj.__arrow_c_stream__(requested_schema=requested_schema)
 
         df = pl.DataFrame({'a': [1, 2, 3, 4], 'b': [5, 6, 7, 8]})
         obj = MyObject(df)
@@ -39,6 +39,12 @@ def __arrow_c_stream__(self):
         assert res.fetchall() == [(1, 5), (2, 6), (3, 7), (4, 8)]
         assert obj.count == 2
 
+        # Ensure __arrow_c_stream__ accepts a requested_schema argument as noop
+        capsule = obj.__arrow_c_stream__(requested_schema="foo")
+        res = duckdb_cursor.sql("select * from capsule")
+        assert res.fetchall() == [(1, 5), (2, 6), (3, 7), (4, 8)]
+        assert obj.count == 3
+
     def test_capsule_roundtrip(self, duckdb_cursor):
         def create_capsule():
             conn = duckdb.connect()
@@ -58,8 +64,8 @@ def __init__(self, rel, conn):
                     self.rel = rel
                     self.conn = conn
 
-                def __arrow_c_stream__(self):
-                    return self.rel.__arrow_c_stream__()
+                def __arrow_c_stream__(self, requested_schema=None):
+                    return self.rel.__arrow_c_stream__(requested_schema=requested_schema)
 
             conn = duckdb.connect()
             rel = conn.sql("select i, i+1, -i from range(100) t(i)")