diff --git a/gunpowder/contrib/nodes/dvid_partner_annotation_source.py b/gunpowder/contrib/nodes/dvid_partner_annotation_source.py
index 400f6c68..36e182e1 100644
--- a/gunpowder/contrib/nodes/dvid_partner_annotation_source.py
+++ b/gunpowder/contrib/nodes/dvid_partner_annotation_source.py
@@ -13,15 +13,17 @@
 
 logger = logging.getLogger(__name__)
 
+
 def strtobool(val):
     val = val.lower()
-    if val in ('y', 'yes', 't', 'true', 'on', '1'):
+    if val in ("y", "yes", "t", "true", "on", "1"):
         return 1
-    elif val in ('n', 'no', 'f', 'false', 'off', '0'):
+    elif val in ("n", "no", "f", "false", "off", "0"):
         return 0
     else:
         raise ValueError(f"Invalid truth value: {val}")
 
+
 class DvidPartnerAnnoationSourceReadException(Exception):
     pass