diff --git a/docs/examples/grocery/grocery.py b/docs/examples/grocery/grocery.py
index 002fafdb..35943171 100644
--- a/docs/examples/grocery/grocery.py
+++ b/docs/examples/grocery/grocery.py
@@ -356,7 +356,7 @@ def customer(self, cust_id, num_items, shop_time):
             for i in range(num_items - 1):
                 yield lane.feed_belt.put((i, None))
             checkout_done = self.env.event()
-            yield lane.feed_belt.put((num_items-1, checkout_done))
+            yield lane.feed_belt.put((num_items - 1, checkout_done))
 
         yield checkout_done
         checkout_time = self.env.now - t0