diff --git a/tools/cal_pos_neg.py b/tools/cal_pos_neg.py
index 702bf1080f750b144ee7c776008919be7f1dc336..3783bf542c8867f244910c1ce764e4fc6e450135 100644
--- a/tools/cal_pos_neg.py
+++ b/tools/cal_pos_neg.py
@@ -11,7 +11,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-#!/usr/bin/python  
+#!/usr/bin/python   
 #-*- coding:utf-8 -*-   
 """
 docstring