diff --git a/bot.py b/bot.py
index 8bed9e8..f35a0e8 100644
--- a/bot.py
+++ b/bot.py
@@ -21,51 +21,51 @@ users = {}
 
 class Kuser:
     def __init__(self, userid, username='', password='', status='第一次用', question='題外'):
-        self._userid = userid
-        self._username = username
-        self._password = password
-        self._status = status
-        self._question = question
-        self._api = KCOJ(URL)
+        self.userid = userid
+        self.username = username
+        self.password = password
+        self.status = status
+        self.question = question
+        self.api = KCOJ(URL)
 
     def new_user(self):
         self.help()
         self.press_username()
     
     def press_username(self):
-        self._status = '輸入學號'
-        self._question = '題外'
-        bot.sendMessage(self._userid, "請輸入您的學號：", reply_markup=ReplyKeyboardRemove())
+        self.status = '輸入學號'
+        self.question = '題外'
+        bot.sendMessage(self.userid, "請輸入您的學號：", reply_markup=ReplyKeyboardRemove())
 
     def press_password(self, text):
-        self._status = '輸入密碼'
-        self._question = '題外'
-        self._username = text
-        bot.sendMessage(self._userid, 
+        self.status = '輸入密碼'
+        self.question = '題外'
+        self.username = text
+        bot.sendMessage(self.userid, 
             "輸入完可刪除訊息以策安全！\n"
             "請輸入您的密碼：", reply_markup=ReplyKeyboardRemove())
 
     def press_oldpassword(self):
-        self._status = '舊的密碼'
-        self._question = '題外'
-        bot.sendMessage(self._userid, 
+        self.status = '舊的密碼'
+        self.question = '題外'
+        bot.sendMessage(self.userid, 
             "請輸入要原本的舊密碼：",
             reply_markup=ReplyKeyboardMarkup(keyboard=[
                 ["首頁🏠"]
             ], resize_keyboard=True))
 
     def press_newpassword(self, text):
-        if text != self._password:
-            self._status = '正常使用'
-            self._question = '題外'
-            bot.sendMessage(self._userid, "密碼錯誤！",
+        if text != self.password:
+            self.status = '正常使用'
+            self.question = '題外'
+            bot.sendMessage(self.userid, "密碼錯誤！",
                 reply_markup=ReplyKeyboardMarkup(keyboard=[
                     ["首頁🏠"]
                 ], resize_keyboard=True))
         else:
-            self._status = '修改密碼'
-            self._question = '題外'
-            bot.sendMessage(self._userid, 
+            self.status = '修改密碼'
+            self.question = '題外'
+            bot.sendMessage(self.userid, 
                 "使用此功能請務必小心！\n"
                 "請輸入要設定的新密碼：",
                 reply_markup=ReplyKeyboardMarkup(keyboard=[
@@ -73,51 +73,51 @@ class Kuser:
                 ], resize_keyboard=True))
         
     def change_password(self, text):
-        self._status = '正常使用'
-        self._question = '題外'
-        self._password = text
-        bot.sendMessage(self._userid, 
-            "修改成功！" if self._api.change_password(self._password) == True else "修改失敗。",
+        self.status = '正常使用'
+        self.question = '題外'
+        self.password = text
+        bot.sendMessage(self.userid, 
+            "修改成功！" if self.api.change_password(self.password) == True else "修改失敗。",
             reply_markup=ReplyKeyboardMarkup(keyboard=[
                 ["首頁🏠"]
             ], resize_keyboard=True))
 
     def login(self, text):
-        self._status = '正常使用'
-        self._question = '題外'
-        self._password = text
-        bot.sendMessage(self._userid, "登入中...", reply_markup=ReplyKeyboardRemove())
-        if self.check_online(self._userid) == True:
-            self.show_homepage(self._userid)
+        self.status = '正常使用'
+        self.question = '題外'
+        self.password = text
+        bot.sendMessage(self.userid, "登入中...", reply_markup=ReplyKeyboardRemove())
+        if self.check_online(self.userid) == True:
+            self.show_homepage(self.userid)
 
     def login_failed(self, chat_id, message_id):
-        self._status = '正常使用'
-        self._question = '題外'
-        if chat_id != self._userid:
+        self.status = '正常使用'
+        self.question = '題外'
+        if chat_id != self.userid:
             bot.sendMessage(chat_id, "登入失敗，請先私訊我重新登入 KCOJ", reply_to_message_id=message_id)
-        bot.sendMessage(self._userid, "哇...登入失敗，讓我們重新開始", reply_markup=ReplyKeyboardRemove())
+        bot.sendMessage(self.userid, "哇...登入失敗，讓我們重新開始", reply_markup=ReplyKeyboardRemove())
         self.press_username()
         
     def connect_failed(self, chat_id, message_id):
-        self._status = '正常使用'
-        self._question = '題外'
-        if chat_id != self._userid:
+        self.status = '正常使用'
+        self.question = '題外'
+        if chat_id != self.userid:
             bot.sendMessage(chat_id, "KCOJ 離線中！請稍後再試", reply_to_message_id=message_id)
         else:
-            bot.sendMessage(self._userid, "KCOJ 離線中！請稍後再試",
+            bot.sendMessage(self.userid, "KCOJ 離線中！請稍後再試",
                 reply_markup=ReplyKeyboardMarkup(keyboard=[
                     ["首頁🏠", "幫助📚"]
                 ], resize_keyboard=True))
 
     def check_online(self, chat_id, message_id=''):
-        result = self._api.check_online()
+        result = self.api.check_online()
         if result == None:
             self.connect_failed(chat_id, message_id)
             return False
         else:
             if result == False:
-                self._api.login(self._username, self._password, 2)
-                result = self._api.check_online()
+                self.api.login(self.username, self.password, 2)
+                result = self.api.check_online()
             if result == False:
                 self.login_failed(chat_id, message_id)
             elif result == None:
@@ -125,15 +125,15 @@ class Kuser:
             return result == True
 
     def logout(self):
-        self._status = '正常使用'
-        self._question = '題外'
-        bot.sendMessage(self._userid, "您現在已經是登出的狀態。", reply_markup=ReplyKeyboardRemove())
+        self.status = '正常使用'
+        self.question = '題外'
+        bot.sendMessage(self.userid, "您現在已經是登出的狀態。", reply_markup=ReplyKeyboardRemove())
         self.press_username()
 
     def show_homepage(self, chat_id):
-        self._status = '正常使用'
-        self._question = '題外'
-        q_dict = self._api.list_questions()
+        self.status = '正常使用'
+        self.question = '題外'
+        q_dict = self.api.list_questions()
         q_str = ''
         for key in q_dict.keys():
             if q_dict[key][1] == '期限未到':
@@ -141,7 +141,7 @@ class Kuser:
                 q_str += "⚠️" if q_dict[key][2] == '未繳' else "✅"
                 q_str += "  /question_" + key + "\n\n"
         bot.sendMessage(chat_id, 
-            "💁 <b>" + self._username + "</b> " + NAME + "\n"
+            "💁 <b>" + self.username + "</b> " + NAME + "\n"
             "➖➖➖➖➖\n"
             "📝<i>可繳交的作業</i>\n\n" + q_str + \
             "➖➖➖➖➖\n" + choice(promote.sentences),
@@ -149,13 +149,13 @@ class Kuser:
             reply_markup=ReplyKeyboardMarkup(keyboard=[
                 ["題庫📝"],
                 ["登出🚪", "改密碼💱", "幫助📚"]
-            ], resize_keyboard=True) if chat_id == self._userid else ReplyKeyboardRemove(),
+            ], resize_keyboard=True) if chat_id == self.userid else ReplyKeyboardRemove(),
             disable_web_page_preview=False)
 
     def list_questions(self, chat_id):
-        self._status = '正常使用'
-        self._question = '題外'
-        q_dict = self._api.list_questions()
+        self.status = '正常使用'
+        self.question = '題外'
+        q_dict = self.api.list_questions()
         q_str = ''
         for key in q_dict.keys():
             q_str += "📗" if q_dict[key][1] == '期限未到' else "📕"
@@ -163,7 +163,7 @@ class Kuser:
             q_str += "⚠️" if q_dict[key][2] == '未繳' else "✅"
             q_str += "  /question_" + key + "\n\n"
         reply = bot.sendMessage(chat_id, 
-            "💁 <b>" + self._username + "</b> " + NAME + "\n"
+            "💁 <b>" + self.username + "</b> " + NAME + "\n"
             "➖➖➖➖➖\n"
             "📝<i>所有作業</i>\n\n" + q_str + \
             "➖➖➖➖➖\n" + choice(promote.sentences),
@@ -171,21 +171,21 @@ class Kuser:
             reply_markup=ReplyKeyboardMarkup(keyboard=[
                 ["首頁🏠", "更新🔃"],
                 ["登出🚪", "改密碼💱", "幫助📚"]
-            ], resize_keyboard=True) if chat_id == self._userid else ReplyKeyboardRemove(),
+            ], resize_keyboard=True) if chat_id == self.userid else ReplyKeyboardRemove(),
             disable_web_page_preview=False)
         bot.sendMessage(chat_id, "點我到題庫頂", reply_to_message_id=reply['message_id'])
 
     def show_question(self, number, chat_id):
-        self._status = '查看題目'
-        self._question = number
+        self.status = '查看題目'
+        self.question = number
         if number in external.QUESTION:
             ext_q = True
             content = external.QUESTION[number]
         else:
             ext_q = False
-            content = '```\n' + self._api.show_question(number) + '\n```'
-        q = self._api.list_questions()[number]
-        q_str = "💁 *" + self._username + "* [" + NAME + "]\n"
+            content = '```\n' + self.api.show_question(number) + '\n```'
+        q = self.api.list_questions()[number]
+        q_str = "💁 *" + self.username + "* [" + NAME + "]\n"
         q_str += "➖➖➖➖➖\n"
         q_str += "📗" if q[1] == '期限未到' else "📕"
         q_str += "*" + number + "* (DL: " + q[0] + ")\n [[[" + q[3] + "]]] [[[" + q[2] + "]]]"
@@ -196,12 +196,12 @@ class Kuser:
                 ["首頁🏠", "題庫📝"],
                 ["交作業📮" if q[1] == '期限未到' else '', "看結果☑️" if q[2] == '已繳' else '', "通過者🌐"],
                 ["登出🚪", "改密碼💱", "幫助📚"]
-            ], resize_keyboard=True) if chat_id == self._userid else ReplyKeyboardRemove())
+            ], resize_keyboard=True) if chat_id == self.userid else ReplyKeyboardRemove())
         if ext_q == False:
             bot.sendMessage(chat_id, "點我到題目頂", reply_to_message_id=reply['message_id'])
 
     def help(self):
-        bot.sendMessage(self._userid, 
+        bot.sendMessage(self.userid, 
             "這裡是 Kuo C Online Judge Bot！\n"
             "可以簡稱 KCOJ Bot，目前定居於 [" + NAME + "]\n"
             "作用是讓大家可以方便的透過我使用郭老程設課的 Online Judge\n"
@@ -223,27 +223,27 @@ class Kuser:
             parse_mode='Markdown')
 
     def upload_answer(self):
-        self._status = '上傳答案'
-        q = self._api.list_questions()[self._question]
-        q_str = "💁 <b>" + self._username + "</b> " + NAME + "\n"
+        self.status = '上傳答案'
+        q = self.api.list_questions()[self.question]
+        q_str = "💁 <b>" + self.username + "</b> " + NAME + "\n"
         q_str += "➖➖➖➖➖\n"
         q_str += "📗" if q[1] == '期限未到' else "📕"
-        q_str += "<b>" + self._question + "</b> (DL: " + q[0] + ")\n [[" + q[3] + "]] [[" + q[2] + "]]"
+        q_str += "<b>" + self.question + "</b> (DL: " + q[0] + ")\n [[" + q[3] + "]] [[" + q[2] + "]]"
         q_str += "⚠️" if q[2] == '未繳' else "✅"
-        bot.sendMessage(self._userid, 
+        bot.sendMessage(self.userid, 
             q_str + "\n\n現在請把你的程式碼讓我看看（請別超過 20 MB）\n"
             "可以使用「文字訊息」或是「傳送檔案」的方式\n"
             "（注意：可在程式碼前後加上單獨成行的 ``` 避免可能的錯誤。）", parse_mode='HTML',
             reply_markup=ReplyKeyboardMarkup(keyboard=[
-                ["刪除作業⚔️"] if self._api.list_questions()[self._question][2] == '已繳' else [],
+                ["刪除作業⚔️"] if self.api.list_questions()[self.question][2] == '已繳' else [],
                 ["首頁🏠", "回題目📜"]
             ], resize_keyboard=True))
 
     def send_answer(self, text, file_id):
-        self._status = '正常使用'
+        self.status = '正常使用'
         # define filename
-        filename = sys.path[0] + '/' + self._username + self._question
-        if self._api.list_questions()[self._question][3] == 'Python':
+        filename = sys.path[0] + '/' + self.username + self.question
+        if self.api.list_questions()[self.question][3] == 'Python':
             filename += '.py'
         else:
             filename += '.c'
@@ -253,16 +253,16 @@ class Kuser:
                 f.write(text)
         else:
             bot.download_file(file_id, filename)
-        self._api.delete_answer(self._question)
-        if self._api.upload_answer(self._question, filename) == True:
-            bot.sendMessage(self._userid, "上傳成功",
+        self.api.delete_answer(self.question)
+        if self.api.upload_answer(self.question, filename) == True:
+            bot.sendMessage(self.userid, "上傳成功",
                 reply_markup=ReplyKeyboardMarkup(keyboard=[
                     ["首頁🏠", "回題目📜"],
                     ["看結果☑️"],
                     ["登出🚪", "改密碼💱", "幫助📚"]
                 ], resize_keyboard=True))
         else:
-            bot.sendMessage(self._userid, "上傳失敗",
+            bot.sendMessage(self.userid, "上傳失敗",
                 reply_markup=ReplyKeyboardMarkup(keyboard=[
                     ["首頁🏠", "回題目📜"],
                     ["登出🚪", "改密碼💱", "幫助📚"]
@@ -270,51 +270,51 @@ class Kuser:
         os.remove(filename)    
     
     def delete_answer(self):
-        bot.sendMessage(self._userid, "移除成功" if self._api.delete_answer(self._question) == True else "移除失敗",
+        bot.sendMessage(self.userid, "移除成功" if self.api.delete_answer(self.question) == True else "移除失敗",
             reply_markup=ReplyKeyboardMarkup(keyboard=[
                 ["首頁🏠", "回題目📜"],
                 ["登出🚪", "改密碼💱", "幫助📚"]
             ], resize_keyboard=True))
 
     def send_failed(self):
-        self._status = '正常使用'
-        bot.sendMessage(self._userid, "檔案不能超過 20 MB！上傳失敗",
+        self.status = '正常使用'
+        bot.sendMessage(self.userid, "檔案不能超過 20 MB！上傳失敗",
             reply_markup=ReplyKeyboardMarkup(keyboard=[
                 ["首頁🏠", "回題目📜"],
                 ["登出🚪", "改密碼💱", "幫助📚"]
             ], resize_keyboard=True))
 
     def list_passers(self):
-        self._status = '正常使用'
-        q = self._api.list_questions()[self._question]
-        q_str = "💁 <b>" + self._username + "</b> " + NAME + "\n"
+        self.status = '正常使用'
+        q = self.api.list_questions()[self.question]
+        q_str = "💁 <b>" + self.username + "</b> " + NAME + "\n"
         q_str += "➖➖➖➖➖\n"
         q_str += "📗" if q[1] == '期限未到' else "📕"
-        q_str += "<b>" + self._question + "</b> (DL: " + q[0] + ")\n [[" + q[3] + "]] [[" + q[2] + "]]"
+        q_str += "<b>" + self.question + "</b> (DL: " + q[0] + ")\n [[" + q[3] + "]] [[" + q[2] + "]]"
         q_str += "⚠️" if q[2] == '未繳' else "✅"
         q_str += "<code>\n"
-        for passer in self._api.list_passers(self._question):
+        for passer in self.api.list_passers(self.question):
             q_str += "\n" + passer
-        reply = bot.sendMessage(self._userid, q_str + "</code>", 
+        reply = bot.sendMessage(self.userid, q_str + "</code>", 
             parse_mode='HTML',
             reply_markup=ReplyKeyboardMarkup(keyboard=[
                 ["首頁🏠", "回題目📜"],
                 ["登出🚪", "改密碼💱", "幫助📚"]
             ], resize_keyboard=True))
-        bot.sendMessage(self._userid, "點我到名單頂", reply_to_message_id=reply['message_id'])
+        bot.sendMessage(self.userid, "點我到名單頂", reply_to_message_id=reply['message_id'])
 
     def list_results(self):
-        self._status = '正常使用'
-        q = self._api.list_questions()[self._question]
-        q_str = "💁 <b>" + self._username + "</b> " + NAME + "\n"
+        self.status = '正常使用'
+        q = self.api.list_questions()[self.question]
+        q_str = "💁 <b>" + self.username + "</b> " + NAME + "\n"
         q_str += "➖➖➖➖➖\n"
         q_str += "📗" if q[1] == '期限未到' else "📕"
-        q_str += "<b>" + self._question + "</b> (DL: " + q[0] + ")\n"
-        for result in self._api.list_results(self._question, self._username):
+        q_str += "<b>" + self.question + "</b> (DL: " + q[0] + ")\n"
+        for result in self.api.list_results(self.question, self.username):
             q_str += "\n測試編號 <code>" + result[0] + "</code>："
             q_str += "✔️ " if result[1] == '通過測試' else "❌ "
             q_str += result[1]
-        bot.sendMessage(self._userid, q_str, 
+        bot.sendMessage(self.userid, q_str, 
             parse_mode='HTML', 
             reply_markup=ReplyKeyboardMarkup(keyboard=[
                 ["首頁🏠", "回題目📜"],
@@ -343,7 +343,7 @@ def on_chat(msg):
         last_name = ''
     print("😊 student_name:", msg['from']['first_name'], last_name, "😊")
     # id
-    print("😯 student_id:", user._username, "😯")
+    print("😯 student_id:", user.username, "😯")
     print()
     # ==========================================================
 
@@ -365,17 +365,17 @@ def on_chat(msg):
                 user.help()
 
         # first-time user
-        elif user._status == '第一次用':
+        elif user.status == '第一次用':
             if chat_type == 'private':
                 user.new_user()
 
         # press password
-        elif user._status == '輸入學號':
+        elif user.status == '輸入學號':
             if chat_type == 'private':
                 user.press_password(msg['text'])
 
         # login
-        elif user._status == '輸入密碼':
+        elif user.status == '輸入密碼':
             if chat_type == 'private':
                 user.login(msg['text'])
 
@@ -401,35 +401,35 @@ def on_chat(msg):
                 users[str(from_id)] = user
                 user.logout()
 
-            elif (command[0] == '/delete' or command[0] == '刪除作業⚔️') and user._question != '題外':
+            elif (command[0] == '/delete' or command[0] == '刪除作業⚔️') and user.question != '題外':
                 if user.check_online(chat_id, msg['message_id']) == True:
                     user.delete_answer()
 
-            elif (command[0] == '/upload' or command[0] == '交作業📮') and user._question != '題外':
+            elif (command[0] == '/upload' or command[0] == '交作業📮') and user.question != '題外':
                 if user.check_online(chat_id, msg['message_id']) == True:
                     user.upload_answer()
 
-            elif (command[0] == '/result' or command[0] == '看結果☑️') and user._question != '題外':
+            elif (command[0] == '/result' or command[0] == '看結果☑️') and user.question != '題外':
                 if user.check_online(chat_id, msg['message_id']) == True:
                     user.list_results()
 
-            elif (command[0] == '/passer' or command[0] == '通過者🌐') and user._question != '題外':
+            elif (command[0] == '/passer' or command[0] == '通過者🌐') and user.question != '題外':
                 if user.check_online(chat_id, msg['message_id']) == True:
                     user.list_passers()
 
-            elif command[0] == '回題目📜' and user._question != '題外':
+            elif command[0] == '回題目📜' and user.question != '題外':
                 if user.check_online(chat_id, msg['message_id']) == True:
-                    user.show_question(user._question, chat_id)
+                    user.show_question(user.question, chat_id)
 
-            elif user._status == '舊的密碼':
+            elif user.status == '舊的密碼':
                 if user.check_online(chat_id, msg['message_id']) == True:
                     user.press_newpassword(msg['text'])
 
-            elif user._status == '修改密碼':
+            elif user.status == '修改密碼':
                 if user.check_online(chat_id, msg['message_id']) == True:
                     user.change_password(msg['text'])
 
-            elif user._status == '上傳答案':
+            elif user.status == '上傳答案':
                 if user.check_online(chat_id, msg['message_id']) == True:
                     user.send_answer(msg['text'], '')
 
@@ -438,7 +438,7 @@ def on_chat(msg):
                     bot.sendMessage(chat_id, "(ˊ・ω・ˋ)")
             
     elif content_type == 'document':
-        if user._status == '上傳答案' or user._status == '查看題目':
+        if user.status == '上傳答案' or user.status == '查看題目':
             if user.check_online(chat_id, msg['message_id']) == True:
                 if msg['document']['file_size'] > 167770000:
                     user.send_failed()
@@ -450,11 +450,11 @@ def backup_db():
     for key in users.keys():
         user = users[key]
         users_backup[key] = {
-            'userid': user._userid,
-            'username': user._username,
-            'password': user._password,
-            'status': user._status,
-            'question': user._question
+            'userid': user.userid,
+            'username': user.username,
+            'password': user.password,
+            'status': user.status,
+            'question': user.question
         }
     with open(sys.path[0] + '/users.json', 'w') as f:
         json.dump(users_backup, f, indent='  ')
diff --git a/kcoj.py b/kcoj.py
index 9acf4f2..cc86969 100644
--- a/kcoj.py
+++ b/kcoj.py
@@ -4,22 +4,22 @@ from bs4 import BeautifulSoup
 
 class KCOJ:
     def __init__(self, url):
-        self._url = url
-        self._session = requests.Session()
+        self.url = url
+        self.session = requests.Session()
     # login KCOJ
     def login(self, username, password, course):
         try:
             payload = {'name': username, 
                        'passwd': password,
                        'rdoCourse': course}
-            return self._session.post(self._url + '/Login', data=payload, timeout=0.5)
+            return self.session.post(self.url + '/Login', data=payload, timeout=0.5)
         except requests.exceptions.Timeout:
             return None
 
     # check online status
     def check_online(self):
         try:
-            response = self._session.get(self._url + '/TopMenu', timeout=0.5)
+            response = self.session.get(self.url + '/TopMenu', timeout=0.5)
             soup = BeautifulSoup(response.text, 'html.parser')
             return soup.find('a').get_text().strip() == '線上考試'
         except requests.exceptions.Timeout:
@@ -29,7 +29,7 @@ class KCOJ:
     def list_questions(self):
         try:
             questions = {}
-            response = self._session.get(self._url + '/HomeworkBoard', timeout=0.5)
+            response = self.session.get(self.url + '/HomeworkBoard', timeout=0.5)
             soup = BeautifulSoup(response.text, 'html.parser')
             for tag in soup.find_all('tr'):
                 if tag.find('a') == None:
@@ -48,7 +48,7 @@ class KCOJ:
     # show the content of the question
     def show_question(self, number):
         try:
-            response = self._session.get(self._url + '/showHomework', params={'hwId': number}, timeout=0.5)
+            response = self.session.get(self.url + '/showHomework', params={'hwId': number}, timeout=0.5)
             soup = BeautifulSoup(response.text, 'html.parser')
             raw = soup.find('body').get_text().replace('繳交作業', '').strip()
             content = ''
@@ -62,7 +62,7 @@ class KCOJ:
     def list_passers(self, number):
         try:
             passers = []
-            response = self._session.get(self._url + '/success.jsp', params={'HW_ID': number}, timeout=0.5)
+            response = self.session.get(self.url + '/success.jsp', params={'HW_ID': number}, timeout=0.5)
             soup = BeautifulSoup(response.text, 'html.parser')
             for tr in soup.find_all('tr'):
                 passer = tr.get_text().replace('\n', '').strip()
@@ -76,7 +76,7 @@ class KCOJ:
     def list_results(self, number, username):
         try:
             results = []
-            response = self._session.get(self._url + '/CheckResult.jsp', params={'questionID': number, 'studentID': username}, timeout=0.5)
+            response = self.session.get(self.url + '/CheckResult.jsp', params={'questionID': number, 'studentID': username}, timeout=0.5)
             soup = BeautifulSoup(response.text, 'html.parser')
             for tr in soup.find_all('tr'):
                 td = tr.find('td')
@@ -91,7 +91,7 @@ class KCOJ:
         try:
             payload = {'pass': password, 
                        'submit': 'sumit'}
-            response = self._session.post(self._url + '/changePasswd', data=payload, timeout=0.5)
+            response = self.session.post(self.url + '/changePasswd', data=payload, timeout=0.5)
             soup = BeautifulSoup(response.text, 'html.parser')
             return str(soup.find('body')).split()[-2].strip() == 'Success'
         except requests.exceptions.Timeout:
@@ -100,7 +100,7 @@ class KCOJ:
     # delete the answer of the question
     def delete_answer(self, number):
         try:
-            response = self._session.get(self._url + '/delHw', params={'title': number}, timeout=0.5)
+            response = self.session.get(self.url + '/delHw', params={'title': number}, timeout=0.5)
             soup = BeautifulSoup(response.text, 'html.parser')
             return soup.find('body').get_text().replace('\n', '').strip() == 'delete success'
         except requests.exceptions.Timeout:
@@ -109,8 +109,8 @@ class KCOJ:
     # hand in a answer
     def upload_answer(self, number, file_path):
         try:
-            self._session.get(self._url + '/upLoadHw', params={'hwId': number}, timeout=0.5)
-            response = self._session.post(self._url + '/upLoadFile', 
+            self.session.get(self.url + '/upLoadHw', params={'hwId': number}, timeout=0.5)
+            response = self.session.post(self.url + '/upLoadFile', 
                 data={'FileDesc': 'Send from kcoj_bot'},
                 files={'hwFile': open(file_path, 'rb')},
                 timeout=0.5)