Fixes #232

stix2/datastore/filesystem.py

@@ -15,7 +15,7 @@
 from stix2 import v20, v21
 from stix2.base import _STIXBase
 from stix2.core import parse
-from stix2.datastore import DataSink, DataSource, DataStoreMixin
+from stix2.datastore import DataSink, DataSource, DataStoreMixin, DataSourceError
 from stix2.datastore.filters import Filter, FilterSet, apply_common_filters
 from stix2.utils import format_datetime, get_type_from_id, is_marking
 
@@ -546,7 +546,7 @@ def _check_path_and_write(self, stix_obj, encoding='utf-8'):
 
         # TODO: Better handling of the overwriting case.
         if os.path.isfile(file_path):
-            print("Attempted to overwrite file!", file_path, file=sys.stderr)
+            raise DataSourceError("Attempted to overwrite file (!) at: {}".format(file_path))
         else:
             with io.open(file_path, 'w', encoding=encoding) as f:
                 stix_obj = stix_obj.serialize(pretty=True, encoding=encoding, ensure_ascii=False)