diff --git a/homeassistant/components/sensor/gtfs.py b/homeassistant/components/sensor/gtfs.py
index 16d7268afa3..0d6ac803abb 100644
--- a/homeassistant/components/sensor/gtfs.py
+++ b/homeassistant/components/sensor/gtfs.py
@@ -227,7 +227,7 @@ class GTFSDepartureSensor(Entity):
                         for col in resource.__table__.columns.keys())
 
         def append_keys(resource, prefix=None):
-            """Properly format key val pairs to append to attributes"""
+            """Properly format key val pairs to append to attributes."""
             for key, val in resource.items():
                 if val == "" or val is None or key == "feed_id":
                     continue