[DuckDBPyType] Add __hash__ method overload (duckdb#61)

This PR fixes
https://github.com/duckdb/duckdb/issues/19018#issuecomment-3299362636

Author: evertlammerts

src/duckdb_py/typing/pytype.cpp

@@ -330,6 +330,9 @@ void DuckDBPyType::Initialize(py::handle &m) {
 	                py::is_operator());
 	type_module.def("__eq__", &DuckDBPyType::EqualsString, "Compare two types for equality", py::arg("other"),
 	                py::is_operator());
+	type_module.def("__hash__", [](const DuckDBPyType &type) {
+		return py::hash(py::str(type.ToString()));
+	});
 	type_module.def_property_readonly("id", &DuckDBPyType::GetId);
 	type_module.def_property_readonly("children", &DuckDBPyType::Children);
 	type_module.def(py::init<>([](const string &type_str, shared_ptr<DuckDBPyConnection> connection = nullptr) {

tests/fast/test_type.py

@@ -214,6 +214,20 @@ def test_struct_from_dict(self):
         res = duckdb.list_type({'a': VARCHAR, 'b': VARCHAR})
         assert res == 'STRUCT(a VARCHAR, b VARCHAR)[]'
 
+    def test_hash_method(self):
+        type1 = duckdb.list_type({'a': VARCHAR, 'b': VARCHAR})
+        type2 = duckdb.list_type({'b': VARCHAR, 'a': VARCHAR})
+        type3 = VARCHAR
+
+        type_set = set()
+        type_set.add(type1)
+        type_set.add(type2)
+        type_set.add(type3)
+
+        type_set.add(type1)
+        expected = ['STRUCT(a VARCHAR, b VARCHAR)[]', 'STRUCT(b VARCHAR, a VARCHAR)[]', 'VARCHAR']
+        assert sorted([str(x) for x in list(type_set)]) == expected
+
     # NOTE: we can support this, but I don't think going through hoops for an outdated version of python is worth it
     @pytest.mark.skipif(sys.version_info < (3, 9), reason="python3.7 does not store Optional[..] in a recognized way")
     def test_optional(self):