diff --git a/api/ncnu.py b/api/ncnu.py
index eee08a8..294929e 100644
--- a/api/ncnu.py
+++ b/api/ncnu.py
@@ -3,14 +3,23 @@ from api.tools import *
 
 class NCNU():
     def __init__(self, username, password):
+        '''
+            initial 就登入
+            根據 self.status 判斷成功與否
+        '''
         self.session = requests.Session()
         self.status = self.login(username, password)
     
     def login(self, username, password):
+        '''
+            登入教務系統
+            return bool
+        '''
         # get login token
         response = self.session.get('https://ccweb.ncnu.edu.tw/student/login.php')
         loginToken = find(response, 'input', param={'name': 'token'}).get('value')
 
+        # request login page
         response = self.session.post(
             "https://ccweb.ncnu.edu.tw/student/login.php",
             data={
@@ -21,17 +30,25 @@ class NCNU():
                 'type': 'a'
             }
         )
+        
+        # 成功的話 return http 302, redirect
         if len(response.history)!=0:
             return True
         else:
             return False
 
     def getCourseTable(self, semester):
+        '''
+            下載學期課表
+            儲存在 ./<semester>課表.pdf
+        '''
         url = "https://ccweb.ncnu.edu.tw/student/print_semester_course_list.php"
 
         # get token
         response = self.session.get(url)
         token = find(response, 'input', param={'name': 'token'}).get('value')
+
+        # get pdf binary response 
         response = self.session.post(
             url, 
             data={
@@ -40,6 +57,8 @@ class NCNU():
                 'token': token,
             }
         )
+
+        # save pdf file
         if response.status_code == 200:
             with open('{}課表.pdf'.format(semester), 'wb') as fp:
                 fp.write(response.content)