diff --git a/models/rank/fm/data/get_slot_data.py b/models/rank/fm/data/get_slot_data.py
index 0f0c217d0be374f66cfb3a7445abbff35183e019..f9605d50b6600f1d2bd324b7ab6dd8cc84a6ab49 100644
--- a/models/rank/fm/data/get_slot_data.py
+++ b/models/rank/fm/data/get_slot_data.py
@@ -79,7 +79,7 @@ class Reader(dg.MultiSlotDataGenerator):
                 v = i[1]
                 for j in v:
                     s += " " + k + ":" + str(j)
-            print(s.strip())
+            print(s.strip())  # add print for data preprocessing
 
         return data_iter
 
diff --git a/models/rank/fm/readme.md b/models/rank/fm/readme.md
index 8070671275a48184c6d68a9783796c6600935433..44e7659a80a1bfd080c171f720556ba72408bb3a 100644
--- a/models/rank/fm/readme.md
+++ b/models/rank/fm/readme.md
@@ -151,7 +151,7 @@ class Reader(dg.MultiSlotDataGenerator):
                 v = i[1]
                 for j in v:
                     s += " " + k + ":" + str(j)
-            print(s.strip())
+            print(s.strip()) # add print for data preprocessing
         return data_iter
 reader = Reader(
     "../config.yaml")  # run this file in original folder to find config.yaml