fix lstm alert
diff --git a/python/singa/utils.py b/python/singa/utils.py
index d102771..7dcf8fb 100644
--- a/python/singa/utils.py
+++ b/python/singa/utils.py
@@ -16,7 +16,6 @@
 # =============================================================================
 
 import sys
-import math
 import numpy as np
 import collections