fix python 3.6

Author: chelsea-lin

bigframes/core/utils.py

@@ -254,9 +254,10 @@ def _search_for_nested_json_type(arrow_type: pa.DataType) -> bool:
     if pa.types.is_list(arrow_type):
         return _search_for_nested_json_type(arrow_type.value_type)
     if pa.types.is_struct(arrow_type):
-        return any(
-            _search_for_nested_json_type(field.type) for field in arrow_type.fields
-        )
+        for i in range(arrow_type.num_fields):
+            if _search_for_nested_json_type(arrow_type.field(i).type):
+                return True
+        return False
     return False
 
 

tests/system/small/test_session.py

@@ -884,7 +884,9 @@ def test_read_pandas_w_nested_json_index(session, write_engine):
             pa.list_(pa.struct([("name", bigframes.dtypes.JSON_ARROW_TYPE)]))
         ),
     )
-    with pytest.raises(NotImplementedError, match="Nested JSON types, found in the index"):
+    with pytest.raises(
+        NotImplementedError, match="Nested JSON types, found in the index"
+    ):
         # Until b/401630655 is resolved, json not compatible with allow_large_results=False
         session.read_pandas(pd_idx, write_engine=write_engine).to_pandas(
             allow_large_results=True