diff --git a/test/test_file.py b/test/test_file.py
index 4b893bd..4d0650f 100644
--- a/test/test_file.py
+++ b/test/test_file.py
@@ -16,6 +16,6 @@ log_f = open("1.log","wb")
 log_f.write(words.encode('utf-8'))
 log_f.close()
 
-print('cost ' + tm_cost)
+print('cost ' + str(tm_cost))
 print('speed %s bytes/second' % (len(content)/tm_cost))