diff --git a/stix2/core.py b/stix2/core.py
index 6f05bf9..055a4a6 100644
--- a/stix2/core.py
+++ b/stix2/core.py
@@ -10,7 +10,9 @@ import stix2
 from .base import _Observable, _STIXBase
 from .exceptions import ParseError
 from .markings import _MarkingsMixin
-from .utils import PREFIX_21_REGEX, TYPE_21_REGEX, TYPE_REGEX, EXT_21_REGEX, _get_dict
+from .utils import (
+    EXT_21_REGEX, PREFIX_21_REGEX, TYPE_21_REGEX, TYPE_REGEX, _get_dict,
+)
 
 STIX2_OBJ_MAPS = {}