diff --git a/docs/conf.py b/docs/conf.py
index cc8b8d9..2c57f84 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -23,7 +23,7 @@
 # -- Project information -----------------------------------------------------
 
 project = "dargs"
-copyright = "2020-%d, DeepModeling " % date.today().year
+copyright = "2020-{}, DeepModeling ".format(date.today().year)
 author = "DeepModeling"
 
 # The short X.Y version