diff --git a/app/Article.py b/app/Article.py
index 04a32ea..824df0c 100644
--- a/app/Article.py
+++ b/app/Article.py
@@ -1,3 +1,6 @@
+"""
+This module provides functions about article
+"""
 from WordFreq import WordFreq
 from wordfreqCMD import youdao_link, sort_in_descending_order
 from UseSqlite import InsertQuery, RecordQuery
@@ -46,7 +49,6 @@ def get_today_article(user_word_list, articleID):
     d1 = load_freq_history(path_prefix + 'static/frequency/frequency.p')
     d2 = load_freq_history(path_prefix + 'static/words_and_tests.p')
     d3 = get_difficulty_level(d1, d2)
-
     d = {}
     d_user = load_freq_history(user_word_list)
     user_level = user_difficulty_level(d_user, d3)  # more consideration as user's behaviour is dynamic. Time factor should be considered.
@@ -133,4 +135,4 @@ def get_answer_part(s):
     html_code += '\n'
     html_code += '<button onclick="toggle_visibility(\'answer\');">ANSWER</button>\n'
     html_code += '<div id="answer" style="display:none;">%s</div>\n' % ('\n'.join(result))
-    return html_code
\ No newline at end of file
+    return html_code
diff --git a/app/Login.py b/app/Login.py
index 8e0030b..5ada69f 100644
--- a/app/Login.py
+++ b/app/Login.py
@@ -1,3 +1,6 @@
+"""
+This module provides methods for Login
+"""
 import hashlib
 import string
 from datetime import datetime, timedelta
@@ -7,15 +10,17 @@ path_prefix = '/var/www/wordfreq/wordfreq/'
 path_prefix = './'  # comment this line in deployment
 
 def verify_pass(newpass,oldpass):
-    if(newpass==oldpass):
+    if newpass==oldpass:
         return True
 
-
 def verify_user(username, password):
     rq = RecordQuery(path_prefix + 'static/wordfreqapp.db')
     password = md5(username + password)
-    rq.instructions_with_parameters("SELECT * FROM user WHERE name=:username AND password=:password", dict(
-        username=username, password=password))  # the named style https://docs.python.org/3/library/sqlite3.html
+    rq.instructions_with_parameters(
+        "SELECT * FROM user WHERE name=:username AND password=:password",
+        dict(   # the named style https://docs.python.org/3/library/sqlite3.html
+            username=username,
+            password=password))
     rq.do_with_parameters()
     result = rq.get_results()
     return result != []
@@ -23,12 +28,19 @@ def verify_user(username, password):
 
 def add_user(username, password):
     start_date = datetime.now().strftime('%Y%m%d')
-    expiry_date = (datetime.now() + timedelta(days=30)).strftime('%Y%m%d') # will expire after 30 days
+    # will expire after 30 days
+    expiry_date = (datetime.now() + timedelta(days=30)).strftime('%Y%m%d')
     # 将用户名和密码一起加密，以免暴露不同用户的相同密码
     password = md5(username + password)
     rq = InsertQuery(path_prefix + 'static/wordfreqapp.db')
-    rq.instructions_with_parameters("INSERT INTO user VALUES (:username, :password, :start_date, :expiry_date)", dict(
-        username=username, password=password, start_date=start_date, expiry_date=expiry_date))
+    rq.instructions_with_parameters(
+        "INSERT INTO user VALUES (:username, :password, :start_date, :expiry_date)",
+        dict(
+            username=username,
+            password=password,
+            start_date=start_date,
+            expiry_date=expiry_date
+        ))
     rq.do_with_parameters()
 
 
@@ -96,7 +108,7 @@ class UserName:
         if ' ' in self.username: # a user name must not include a whitespace
             return 'Whitespace is not allowed in the user name.'
         for c in self.username: # a user name must not include special characters, except non-leading periods or underscores
-            if c in string.punctuation and c is not '.' and c is not '_':
+            if c in string.punctuation and c != '.' and c != '_':
                 return f'{c} is not allowed in the user name.'
         if self.username in ['signup', 'login', 'logout', 'reset', 'mark', 'back', 'unfamiliar', 'familiar', 'del']:
             return 'You used a restricted word as your user name.  Please come up with a better one.'
@@ -110,4 +122,3 @@ class WarningMessage:
 
     def __str__(self):
         return UserName(self.s).validate()
-
diff --git a/app/WordFreq.py b/app/WordFreq.py
index 3620a41..766ecaf 100644
--- a/app/WordFreq.py
+++ b/app/WordFreq.py
@@ -2,9 +2,12 @@
 # Copyright 2019 (C) Hui Lan <hui.lan@cantab.net>
 # Written permission must be obtained from the author for commercial uses.
 ###########################################################################
-
-from wordfreqCMD import remove_punctuation, freq, sort_in_descending_order
+"""
+This module produces word frequency
+"""
 import string
+from wordfreqCMD import remove_punctuation, freq, sort_in_descending_order
+
 
 class WordFreq:
     def __init__(self, s):
@@ -17,9 +20,8 @@ class WordFreq:
             if len(word) > 0 and word[0] in string.ascii_letters:
                 lst.append(t)
         return sort_in_descending_order(lst)
-    
+
 
 if __name__ == '__main__':
     f = WordFreq('BANANA; Banana, apple ORANGE Banana banana.')
     print(f.get_freq())
-
diff --git a/app/account_service.py b/app/account_service.py
index 9b1c46b..eace163 100644
--- a/app/account_service.py
+++ b/app/account_service.py
@@ -1,54 +1,54 @@
+"""
+This module provides services about account.
+"""
 from flask import *
-from Login import check_username_availability, verify_user, add_user, get_expiry_date, change_password, WarningMessage
+from Login import check_username_availability, \
+    verify_user, add_user, get_expiry_date, change_password, WarningMessage
 
 
 # 初始化蓝图
 accountService = Blueprint("accountService", __name__)
 
-### Sign-up, login, logout ###
+
+# Sign-up, login, logout
 @accountService.route("/signup", methods=['GET', 'POST'])
 def signup():
     '''
     注册
     :return: 根据注册是否成功返回不同界面
     '''
+    # GET方法直接返回注册页面
     if request.method == 'GET':
-        # GET方法直接返回注册页面
         return render_template('signup.html')
-    elif request.method == 'POST':
+    if request.method == 'POST':
         # POST方法需判断是否注册成功，再根据结果返回不同的内容
         username = escape(request.form['username'])
         password = escape(request.form['password'])
         password2 = escape(request.form['password2'])
-        
         #! 添加如下代码为了过滤注册时的非法字符
         warn = WarningMessage(username)
         if str(warn) != 'OK':
             return str(warn)
-        
         available = check_username_availability(username)
         if not available: # 用户名不可用
             flash('用户名 %s 已经被注册。' % (username))
             return render_template('signup.html')
-        elif len(password.strip()) < 4: # 密码过短
+        if len(password.strip()) < 4: # 密码过短
             return '密码过于简单。'
-        elif password != password2:
+        if password != password2:
             return '确认密码与输入密码不一致！'
-        else: # 添加账户信息
-            add_user(username, password)
-            verified = verify_user(username, password)
-            if verified:
-                # 写入session
-                session['logged_in'] = True
-                session[username] = username
-                session['username'] = username
-                session['expiry_date'] = get_expiry_date(username)
-                session['articleID'] = None
-                return '<p>恭喜，你已成功注册， 你的用户名是 <a href="%s">%s</a>。</p>\
-                <p><a href="/%s">开始使用</a> <a href="/">返回首页</a><p/>' % (username, username, username)
-            else:
-                return '用户名密码验证失败。'
-
+        add_user(username, password)# 添加账户信息
+        verified = verify_user(username, password)
+        if verified:
+            # 写入session
+            session['logged_in'] = True
+            session[username] = username
+            session['username'] = username
+            session['expiry_date'] = get_expiry_date(username)
+            session['articleID'] = None
+            return '<p>恭喜，你已成功注册， 你的用户名是 <a href="%s">%s</a>。</p>\
+            <p><a href="/%s">开始使用</a> <a href="/">返回首页</a><p/>' % (username, username, username)
+        return '用户名密码验证失败。'
 
 
 @accountService.route("/login", methods=['GET', 'POST'])
@@ -62,11 +62,10 @@ def login():
         if not session.get('logged_in'):
             # 未登录，返回登录页面
             return render_template('login.html')
-        else:
-            # 已登录，提示信息并显示登出按钮
-            return '你已登录 <a href="/%s">%s</a>。 登出点击<a href="/logout">这里</a>。' % (
+        # 已登录，提示信息并显示登出按钮
+        return '你已登录 <a href="/%s">%s</a>。 登出点击<a href="/logout">这里</a>。' % (
                 session['username'], session['username'])
-    elif request.method == 'POST':
+    if request.method == 'POST':
         # POST方法用于判断登录是否成功
         # check database and verify user
         username = escape(request.form['username'])
@@ -81,8 +80,7 @@ def login():
             session['expiry_date'] = user_expiry_date
             session['articleID'] = None
             return redirect(url_for('user_bp.userpage', username=username))
-        else:
-            return '无法通过验证。'
+        return '无法通过验证。'
 
 
 @accountService.route("/logout", methods=['GET', 'POST'])
@@ -111,21 +109,18 @@ def reset():
     if request.method == 'GET':
         # GET请求返回修改密码页面
         return render_template('reset.html', username=session['username'], state='wait')
-    else:
-        # POST请求用于提交修改后信息
-        old_password = escape(request.form['old-password'])
-        new_password = escape(request.form['new-password'])
-
-        re_new_password = escape(request.form['re-new-password'])  # 确认新密码
-        if re_new_password != new_password: #验证新密码两次输入是否相同
-            return '新密码不匹配，请重新输入'
-        if len(new_password) < 4: #验证新密码长度，原则参照注册模块
-            return '密码过于简单。(密码长度至少4位)'
-
-        flag = change_password(username, old_password, new_password) # flag表示是否修改成功
-        if flag:
-            session['logged_in'] = False
-            return \
+    # POST请求用于提交修改后信息
+    old_password = escape(request.form['old-password'])
+    new_password = escape(request.form['new-password'])
+    re_new_password = escape(request.form['re-new-password'])  # 确认新密码
+    if re_new_password != new_password: #验证新密码两次输入是否相同
+        return '新密码不匹配，请重新输入'
+    if len(new_password) < 4: #验证新密码长度，原则参照注册模块
+        return '密码过于简单。(密码长度至少4位)'
+    flag = change_password(username, old_password, new_password) # flag表示是否修改成功
+    if flag:
+        session['logged_in'] = False
+        return \
 '''
 <script>
 alert('密码修改成功，请重新登录。');
@@ -134,8 +129,7 @@ window.location.href="/login";
 
 '''
 
-        else:
-            return \
+
 '''
 <script>
 alert('密码修改失败');
diff --git a/app/difficulty.py b/app/difficulty.py
index 50aa179..30b2716 100644
--- a/app/difficulty.py
+++ b/app/difficulty.py
@@ -3,8 +3,10 @@
 # Written permission must be obtained from the author for commercial uses.
 ###########################################################################
 
-# Purpose: compute difficulty level of a English text
-
+"""
+This module provides functions for calculating user words difficulty
+Purpose: compute difficulty level of a English text
+"""
 import pickle
 import math
 from wordfreqCMD import remove_punctuation, freq, sort_in_descending_order, sort_in_ascending_order
@@ -21,37 +23,36 @@ def difficulty_level_from_frequency(word, d):
     level = 1
     if not word in d:
         return level
-    
-    if 'what' in d:
-        ratio = (d['what']+1)/(d[word]+1) # what is a frequent word
-        level = math.log( max(ratio, 1), 2)
 
-    level = min(level, 8) 
+    if 'what' in d:
+        ratio = (d['what'] + 1) / (d[word] + 1)  # what is a frequent word
+        level = math.log(max(ratio, 1), 2)
+
+    level = min(level, 8)
     return level
 
 
 def get_difficulty_level(d1, d2):
     d = {}
     L = list(d1.keys())  # in d1, we have freuqence for each word
-    L2 = list(d2.keys()) # in d2, we have test types (e.g., CET4,CET6,BBC) for each word
+    L2 = list(d2.keys())  # in d2, we have test types (e.g., CET4,CET6,BBC) for each word
     L.extend(L2)
-    L3 = list(set(L)) # L3 contains all words
+    L3 = list(set(L))  # L3 contains all words
     for k in L3:
         if k in d2:
             if 'CET4' in d2[k]:
-                d[k] = 4 # CET4 word has level 4
+                d[k] = 4  # CET4 word has level 4
             elif 'CET6' in d2[k]:
                 d[k] = 6
             elif 'BBC' in d2[k]:
                 d[k] = 8
-                if k in d1: # BBC could contain easy words that are not in CET4 or CET6.  So 4 is not reasonable.  Recompute difficulty level.
+                if k in d1:  # BBC could contain easy words that are not in CET4 or CET6.  So 4 is not reasonable.  Recompute difficulty level.
                     d[k] = min(difficulty_level_from_frequency(k, d1), d[k])
         elif k in d1:
             d[k] = difficulty_level_from_frequency(k, d1)
 
     return d
 
-        
 
 def revert_dict(d):
     '''
@@ -62,12 +63,13 @@ def revert_dict(d):
     for k in d:
         if type(d[k]) is list:  # d[k] is a list of dates.
             lst = d[k]
-        elif type(d[k]) is int: # for backward compatibility.  d was sth like {'word':1}.  The value d[k] is not a list of dates, but a number representing how frequent this word had been added to the new word book. 
+        elif type(d[
+                      k]) is int:  # for backward compatibility.  d was sth like {'word':1}.  The value d[k] is not a list of dates, but a number representing how frequent this word had been added to the new word book.
             freq = d[k]
-            lst = freq*['2021082019'] # why choose this date?  No particular reasons.  I fix the bug in this date.
+            lst = freq * ['2021082019']  # why choose this date?  No particular reasons.  I fix the bug in this date.
 
         for time_info in lst:
-            date = time_info[:10] # until hour
+            date = time_info[:10]  # until hour
             if not date in d2:
                 d2[date] = [k]
             else:
@@ -76,42 +78,43 @@ def revert_dict(d):
 
 
 def user_difficulty_level(d_user, d):
-    d_user2 = revert_dict(d_user) # key is date, and value is a list of words added in that date
+    d_user2 = revert_dict(d_user)  # key is date, and value is a list of words added in that date
     count = 0
     geometric = 1
-    for date in sorted(d_user2.keys(), reverse=True): # most recently added words are more important while determining user's level
-        lst = d_user2[date] # a list of words
-        lst2 = [] # a list of tuples, (word, difficulty level)
-        for  word in lst:
+    for date in sorted(d_user2.keys(),
+                       reverse=True):  # most recently added words are more important while determining user's level
+        lst = d_user2[date]  # a list of words
+        lst2 = []  # a list of tuples, (word, difficulty level)
+        for word in lst:
             if word in d:
                 lst2.append((word, d[word]))
 
-        lst3 = sort_in_ascending_order(lst2) # easiest tuple first
-        #print(lst3)
+        lst3 = sort_in_ascending_order(lst2)  # easiest tuple first
+        # print(lst3)
         for t in lst3:
             word = t[0]
             hard = t[1]
-            #print('WORD %s HARD %4.2f' % (word, hard))
+            # print('WORD %s HARD %4.2f' % (word, hard))
             geometric = geometric * (hard)
             count += 1
             if count >= 10:
-                return geometric**(1/count)
+                return geometric ** (1 / count)
 
-    return geometric**(1/max(count,1))
+    return geometric ** (1 / max(count, 1))
 
 
 def text_difficulty_level(s, d):
     s = remove_punctuation(s)
     L = freq(s)
 
-    lst = [] # a list of tuples, each tuple being (word, difficulty level)
+    lst = []  # a list of tuples, each tuple being (word, difficulty level)
     for x in L:
         word = x[0]
         if word in d:
             lst.append((word, d[word]))
 
-    lst2 = sort_in_descending_order(lst) # most difficult words on top
-    #print(lst2)
+    lst2 = sort_in_descending_order(lst)  # most difficult words on top
+    # print(lst2)
     count = 0
     geometric = 1
     for t in lst2:
@@ -119,22 +122,18 @@ def text_difficulty_level(s, d):
         hard = t[1]
         geometric = geometric * (hard)
         count += 1
-        if count >= 20: # we look for n most difficult words
-            return geometric**(1/count)
-        
-    return geometric**(1/max(count,1))
+        if count >= 20:  # we look for n most difficult words
+            return geometric ** (1 / count)
 
+    return geometric ** (1 / max(count, 1))
 
 
 if __name__ == '__main__':
-
-
     d1 = load_record('frequency.p')
-    #print(d1)
+    # print(d1)
 
     d2 = load_record('words_and_tests.p')
-    #print(d2)
-
+    # print(d2)
 
     d3 = get_difficulty_level(d1, d2)
 
@@ -197,7 +196,6 @@ Amidst the aftermath of this shocking referendum vote, there is great uncertaint
 
 '''
 
-
     s = '''
 British Prime Minister Boris Johnson walks towards a voting station during the Brexit referendum in Britain, June 23, 2016. (Photo: EPA-EFE)
 
@@ -218,7 +216,6 @@ The prime minister was forced to ask for an extension to Britain's EU departure
 Johnson has repeatedly pledged to finalize the first stage, a transition deal, of Britain's EU divorce battle by Oct. 31. A second stage will involve negotiating its future relationship with the EU on trade, security and other salient issues.
 '''
 
-
     s = '''
 Thank you very much. We have a Cabinet meeting. We’ll have a few questions after grace. And, if you would, Ben, please do the honors.
 
@@ -233,17 +230,9 @@ We need — for our farmers, our manufacturers, for, frankly, unions and non-uni
 
 '''
 
-
-
-
-    #f = open('bbc-fulltext/bbc/entertainment/001.txt')
-    f = open('wordlist.txt')
+    # f = open('bbc-fulltext/bbc/entertainment/001.txt')
+    f = open('wordlist.txt',encoding="utf-8")
     s = f.read()
     f.close()
 
-
-
-    
     print(text_difficulty_level(s, d3))
-
-            
diff --git a/app/main.py b/app/main.py
index e311bb0..98c495e 100644
--- a/app/main.py
+++ b/app/main.py
@@ -52,8 +52,7 @@ def appears_in_test(word, d):
     '''
     if not word in d:
         return ''
-    else:
-        return ','.join(d[word])
+    return ','.join(d[word])
 
 
 @app.route("/mark", methods=['GET', 'POST'])
@@ -71,8 +70,8 @@ def mark_word():
         d = pickle_idea.merge_frequency(lst, lst_history)
         pickle_idea.save_frequency_to_pickle(d, path_prefix + 'static/frequency/frequency.p')
         return redirect(url_for('mainpage'))
-    else: # 不回应GET请求
-        return 'Under construction'
+    # 不回应GET请求
+    return 'Under construction'
 
 
 @app.route("/", methods=['GET', 'POST'])
@@ -92,7 +91,7 @@ def mainpage():
         pickle_idea.save_frequency_to_pickle(d, path_prefix + 'static/frequency/frequency.p')
         return render_template('mainpage_post.html', lst=lst, yml=Yaml.yml)
 
-    elif request.method == 'GET':  # when we load a html page
+    if request.method == 'GET':  # when we load a html page
         random_ads = get_random_ads()
         number_of_essays = total_number_of_essays()
         d = load_freq_history(path_prefix + 'static/frequency/frequency.p')
@@ -102,7 +101,6 @@ def mainpage():
                                d_len=d_len, lst=lst, yml=Yaml.yml)
 
 
-
 if __name__ == '__main__':
     '''
     运行程序
diff --git a/app/pickle_idea.py b/app/pickle_idea.py
index 45bd19a..679b0f9 100644
--- a/app/pickle_idea.py
+++ b/app/pickle_idea.py
@@ -3,16 +3,17 @@
 # Written permission must be obtained from the author for commercial uses.
 ###########################################################################
 
-# Purpose: dictionary & pickle as a simple means of database.
-# Task: incorporate the functions into wordfreqCMD.py such that it will also show cumulative frequency.
-
+"""
+  Purpose: dictionary & pickle as a simple means of database.
+  Task: incorporate the functions into wordfreqCMD.py such that it will also show cumulative frequency.
+"""
 import pickle
 from datetime import datetime
 
 
 def lst2dict(lst, d):
-    ''' 
-    Store the information in list lst to dictionary d. 
+    '''
+    Store the information in list lst to dictionary d.
     Note: nothing is returned.
 
     '''
@@ -20,14 +21,14 @@ def lst2dict(lst, d):
         word = x[0]
         freq = x[1]
         if not word in d:
-            d[word] = freq 
+            d[word] = freq
         else:
             d[word] += freq
 
 
 def dict2lst(d):
     return list(d.items()) # a list of (key, value) pairs
-        
+
 
 def merge_frequency(lst1, lst2):
     d = {}
diff --git a/app/pickle_idea2.py b/app/pickle_idea2.py
index 4055fc4..f41bcd7 100644
--- a/app/pickle_idea2.py
+++ b/app/pickle_idea2.py
@@ -43,7 +43,7 @@ def dict2lst(d):
             for k in d:
                 lst.append((k, [datetime.now().strftime('%Y%m%d%H%M')]))
             return lst
-        elif isinstance(d[keys[0]], list):
+        if isinstance(d[keys[0]], list):
             return list(d.items()) # a list of (key, value) pairs
 
     return []
diff --git a/app/static/js/fillword.js b/app/static/js/fillword.js
index ba249dd..f98dec1 100644
--- a/app/static/js/fillword.js
+++ b/app/static/js/fillword.js
@@ -11,34 +11,39 @@ function getWord() {
 
 function fillInWord() {
     let word = getWord();
-    if (isRead) read(word);
-    if (!isChoose) return;
+    if (isRead) {read(word);}
+    if (!isChoose) {return;}
     const element = document.getElementById("selected-words");
     element.value = element.value + " " + word;
 }
 
-document.getElementById("text-content").addEventListener("click", fillInWord, false);
+document
+    .getElementById("text-content")
+    .addEventListener("click", fillInWord, false);
 
 function makeUtterance(str, rate) {
     let msg = new SpeechSynthesisUtterance(str);
     msg.rate = rate;
     msg.lang = "en-US"; // TODO: add language options menu
-    msg.onboundary = ev => {
-        if (ev.name == "word") {
+    msg.onboundary = function(ev) {
+        if (ev.name === "word") {
             current_position = ev.charIndex;
         }
-    }
+    };
     return msg;
 }
 
 const sliderValue = document.getElementById("rangeValue"); // 显示值
 const inputSlider = document.getElementById("rangeComponent"); // 滑块元素
-inputSlider.oninput = () => {
+inputSlider.oninput = function(){
     let value = inputSlider.value; // 获取滑块的值
-    sliderValue.textContent = value + '×';
-    if (!reader.speaking) return;
+    sliderValue.textContent = value + "×";
+    if (!reader.speaking) {return;}
     reader.cancel();
-    let msg = makeUtterance(to_speak.substring(original_position + current_position), value);
+    let msg = makeUtterance(
+        to_speak.substring(original_position + current_position),
+        value
+    );
     original_position = original_position + current_position;
     current_position = 0;
     reader.speak(msg);
diff --git a/app/static/js/highlight.js b/app/static/js/highlight.js
index 5ec9663..d3e3e3c 100644
--- a/app/static/js/highlight.js
+++ b/app/static/js/highlight.js
@@ -2,44 +2,60 @@ let isHighlight = true;
 
 function cancelBtnHandler() {
     cancelHighlighting();
-    document.getElementById("text-content").removeEventListener("click", fillInWord, false);
-    document.getElementById("text-content").removeEventListener("touchstart", fillInWord, false);
-    document.getElementById("text-content").addEventListener("click", fillInWord2, false);
-    document.getElementById("text-content").addEventListener("touchstart", fillInWord2, false);
+    document
+        .getElementById("text-content")
+        .removeEventListener("click", fillInWord, false);
+    document.getElementById("text-content")
+        .removeEventListener("touchstart", fillInWord, false);
+    document.getElementById("text-content")
+        .addEventListener("click", fillInWord2, false);
+    document.getElementById("text-content")
+        .addEventListener("touchstart", fillInWord2, false);
 }
 
 function showBtnHandler() {
-    document.getElementById("text-content").removeEventListener("click", fillInWord2, false);
-    document.getElementById("text-content").removeEventListener("touchstart", fillInWord2, false);
-    document.getElementById("text-content").addEventListener("click", fillInWord, false);
-    document.getElementById("text-content").addEventListener("touchstart", fillInWord, false);
+    document.getElementById("text-content")
+        .removeEventListener("click", fillInWord2, false);
+    document.getElementById("text-content")
+        .removeEventListener("touchstart", fillInWord2, false);
+    document.getElementById("text-content")
+        .addEventListener("click", fillInWord, false);
+    document.getElementById("text-content")
+        .addEventListener("touchstart", fillInWord, false);
     highLight();
 }
 
 function getWord() {
-    return window.getSelection ? window.getSelection() : document.selection.createRange().text;
+    return (window.getSelection ?
+            window.getSelection() :
+            document.selection.createRange().text);
 }
 
 function highLight() {
-    if (!isHighlight) return;
+    if (!isHighlight) {return;}
     let articleContent = document.getElementById("article").innerText; //将原来的.innerText改为.innerHtml，使用innerText会把原文章中所包含的<br>标签去除，导致处理后的文章内容失去了原来的格式
     let pickedWords = document.getElementById("selected-words");  // words picked to the text area
     let dictionaryWords = document.getElementById("selected-words2"); // words appearing in the user's new words list
     let allWords = "";  //初始化allWords的值，避免进入判断后编译器认为allWords未初始化的问题
-    if(dictionaryWords != null){//增加一个判断，检查生词本里面是否为空，如果为空，allWords只添加选中的单词
+    if(dictionaryWords !== null){//增加一个判断，检查生词本里面是否为空，如果为空，allWords只添加选中的单词
         allWords = pickedWords.value + " " + dictionaryWords.value;
     }
     else{
         allWords = pickedWords.value + " ";
     }
     const list = allWords.split(" ");//将所有的生词放入一个list中，用于后续处理
-    for (let i = 0; i < list.length; ++i) {
-        list[i] = list[i].replace(/(^\s*)|(\s*$)/g, ""); //消除单词两边的空字符
-        list[i] = list[i].replace('|', "");
-        list[i] = list[i].replace('?', "");
-        if (list[i] !== "" && "<mark>".indexOf(list[i]) === -1 && "</mark>".indexOf(list[i]) === -1) {
-	    //将文章中所有出现该单词word的地方改为：" <mark>" + word + "<mark> "。 正则表达式RegExp()中，"\\s"代表单词前后必须要有空格，以防止只对单词中的部分字符高亮的情况出现。
-            articleContent = articleContent.replace(new RegExp("\\s"+list[i]+"\\s", "g"), " <mark>" + list[i] + "</mark> ");
+    for (let i = 0; i < list.length; i+=1) {
+        list[i] = list[i].replace(/(^\s*)|(\s*$)/gm, ""); //消除单词两边的空字符
+        list[i] = list[i].replace("|", "");
+        list[i] = list[i].replace("?", "");
+        if (list[i] !== "" &&
+            "<mark>".indexOf(list[i]) === -1 &&
+            "</mark>".indexOf(list[i]) === -1
+           ) {
+        //将文章中所有出现该单词word的地方改为：" <mark>" + word + "<mark> "。 正则表达式RegExp()中，"\\s"代表单词前后必须要有空格，以防止只对单词中的部分字符高亮的情况出现。
+            articleContent = articleContent.replace(
+                new RegExp("\\s"+list[i]+"\\s", "g"),
+                " <mark>" + list[i] + "</mark> ");
         }
     }
     document.getElementById("article").innerHTML = articleContent;
@@ -48,23 +64,29 @@ function highLight() {
 function cancelHighlighting() {
     let articleContent = document.getElementById("article").innerText;//将原来的.innerText改为.innerHtml，原因同上
     let pickedWords = document.getElementById("selected-words");
-    const dictionaryWords = document.getElementById("selected-words2");    
-    const list = pickedWords.value.split(" ");    
-    if (pickedWords != null) {
-        for (let i = 0; i < list.length; ++i) {
-            list[i] = list[i].replace(/(^\s*)|(\s*$)/g, "");
+    const dictionaryWords = document.getElementById("selected-words2");
+    const list = pickedWords.value.split(" ");
+    if (pickedWords !== null) {
+        for (let i = 0; i < list.length; i+=1) {
+            list[i] = list[i].replace(/(^\s*)|(\s*$)/gm, "");
             if (list[i] !== "") { //原来判断的代码中，替换的内容为“list[i]”这个字符串，这明显是错误的，我们需要替换的是list[i]里的内容
-                articleContent = articleContent.replace(new RegExp("<mark>"+list[i]+"</mark>", "g"), list[i]);
+                articleContent = articleContent.replace(
+                    new RegExp("<mark>"+list[i]+"</mark>", "g"),
+                    list[i]
+                );
             }
         }
     }
-    if (dictionaryWords != null) {
+    if (dictionaryWords !== null) {
         let list2 = pickedWords.value.split(" ");
-        for (let i = 0; i < list2.length; ++i) {
+        for (let i = 0; i < list2.length; i+=1) {
             list2 = dictionaryWords.value.split(" ");
-            list2[i] = list2[i].replace(/(^\s*)|(\s*$)/g, "");
+            list2[i] = list2[i].replace(/(^\s*)|(\s*$)/gm, "");
             if (list2[i] !== "") { //原来代码中，替换的内容为“list[i]”这个字符串，这明显是错误的，我们需要替换的是list[i]里的内容
-                articleContent = articleContent.replace(new RegExp("<mark>"+list2[i]+"</mark>", "g"), list2[i]);
+                articleContent = articleContent.replace(
+                    new RegExp("<mark>"+list2[i]+"</mark>", "g"),
+                    list2[i]
+                );
             }
         }
     }
diff --git a/app/static/js/word_operation.js b/app/static/js/word_operation.js
index ea6a6e8..9a61de1 100644
--- a/app/static/js/word_operation.js
+++ b/app/static/js/word_operation.js
@@ -3,17 +3,17 @@ function familiar(theWord) {
     let word = $("#word_" + theWord).text();
     let freq = $("#freq_" + theWord).text();
     $.ajax({
-        type:"GET",
-        url:"/" + username + "/" + word + "/familiar",
         success:function(response){
             let new_freq = freq - 1;
-            const allow_move = document.getElementById("move_dynamiclly").checked;
+            const allow_move = document
+                .getElementById("move_dynamiclly")
+                .checked;
             if (allow_move) {
 
                 if (new_freq <= 0) {
                     removeWord(theWord);
                 } else {
-                    renderWord({ word: theWord, freq: new_freq });
+                    renderWord({ freq: new_freq,word: theWord });
                 }
             } else {
                 if(new_freq <1) {
@@ -22,7 +22,9 @@ function familiar(theWord) {
                     $("#freq_" + theWord).text(new_freq);
                 }
             }
-        }
+        },
+        type:"GET",
+        url:"/" + username + "/" + word + "/familiar"
     });
 }
 
@@ -31,38 +33,42 @@ function unfamiliar(theWord) {
     let word = $("#word_" + theWord).text();
     let freq = $("#freq_" + theWord).text();
     $.ajax({
-        type:"GET",
-        url:"/" + username + "/" + word + "/unfamiliar",
         success:function(response){
             let new_freq = parseInt(freq) + 1;
-            const allow_move = document.getElementById("move_dynamiclly").checked;
+            const allow_move = document
+                .getElementById("move_dynamiclly")
+                .checked;
             if (allow_move) {
-                renderWord({ word: theWord, freq: new_freq });
+                renderWord({ freq: new_freq,word: theWord  });
             } else {
                 $("#freq_" + theWord).text(new_freq);
             }
-        }
+        },
+        type:"GET",
+        url:"/" + username + "/" + word + "/unfamiliar"
     });
 }
 
 function delete_word(theWord) {
     let username = $("#username").text();
-    let word = theWord.replace('&amp;', '&');
+    let word = theWord.replace("&amp;", "&");
     $.ajax({
-        type:"GET",
-        url:"/" + username + "/" + word + "/del",
         success:function(response){
-            const allow_move = document.getElementById("move_dynamiclly").checked;
+            const allow_move = document
+                .getElementById("move_dynamiclly")
+                .checked;
             if (allow_move) {
                 removeWord(theWord);
             } else {
                 $("#p_" + theWord).remove();
-            }    
-        }
+            }
+        },
+        type:"GET",
+        url:"/" + username + "/" + word + "/del"
     });
 }
 
-/* 
+/*
  * interface Word {
  *   word: string,
  *   freq: number
@@ -75,11 +81,12 @@ function delete_word(theWord) {
 function parseWord(element) {
     const word = element
         .querySelector("a.btn.btn-light[role=button]")  // 获取当前词频元素的词汇元素
-        .innerText  // 获取词汇值;
-    const freq = Number.parseInt(element.querySelector(`#freq_${word}`).innerText);   // 获取词汇的数量
+        .innerText; // 获取词汇值;
+    const freq = Number// 获取词汇的数量
+        .parseInt(element.querySelector(`#freq_${word}`).innerText);
     return {
-        word,
-        freq
+        freq,
+        word
     };
 }
 
@@ -104,7 +111,7 @@ function wordTemplate(word) {
  */
 function removeWord(word) {
     // 根据词频信息删除元素
-    word = word.replace('&amp;', '&');
+    word = word.replace("&amp;", "&");
     const element_to_remove = document.getElementById(`p_${word}`);
     if (element_to_remove != null) {
         element_to_remove.remove();
@@ -134,7 +141,11 @@ function renderWord(word) {
     // 让发生变化的元素抖动
     new_element.classList.add("shaking");
     // 移动到该元素
-    new_element.scrollIntoView({behavior: "smooth", block: "center", inline: "nearest"});
+    new_element.scrollIntoView({
+        behavior: "smooth",
+        block: "center",
+        inline: "nearest"
+    });
     // 抖动完毕后删除抖动类
     setTimeout(() => {
         new_element.classList.remove("shaking");
@@ -145,7 +156,7 @@ function renderWord(word) {
  * 从string中创建一个HTML元素并返回
  */
 function elementFromString(string) {
-    const d = document.createElement('div');
+    const d = document.createElement("div");
     d.innerHTML = string;
     return d.children.item(0);
 }
diff --git a/app/user_service.py b/app/user_service.py
index 2d10404..be075e2 100644
--- a/app/user_service.py
+++ b/app/user_service.py
@@ -1,5 +1,7 @@
+"""
+This module provides methods for user_services
+"""
 from datetime import datetime
-
 from flask import *
 
 # from app import Yaml
@@ -36,6 +38,7 @@ def user_reset(username):
     else:
         return 'Under construction'
 
+
 @userService.route("/<username>/back", methods=['GET'])
 def user_back(username):
     '''
@@ -48,7 +51,6 @@ def user_back(username):
         return redirect(url_for('user_bp.userpage', username=username))
 
 
-
 @userService.route("/<username>/<word>/unfamiliar", methods=['GET', 'POST'])
 def unfamiliar(username, word):
     '''
@@ -141,9 +143,6 @@ def userpage(username):
                                words=words)
 
 
-
-
-
 @userService.route("/<username>/mark", methods=['GET', 'POST'])
 def user_mark_word(username):
     '''
diff --git a/app/wordfreqCMD.py b/app/wordfreqCMD.py
index c4f8a63..09a773e 100644
--- a/app/wordfreqCMD.py
+++ b/app/wordfreqCMD.py
@@ -2,13 +2,16 @@
 # Copyright 2019 (C) Hui Lan <hui.lan@cantab.net>
 # Written permission must be obtained from the author for commercial uses.
 ###########################################################################
-
+"""
+This Module produces word frequency
+"""
 import collections
 import string
 import operator
-import os, sys # 引入模块sys，因为我要用里面的sys.argv列表中的信息来读取命令行参数。
+import os, sys  # 引入模块sys，因为我要用里面的sys.argv列表中的信息来读取命令行参数。
 import pickle_idea
 
+
 def freq(fruit):
     '''
     功能： 把字符串转成列表。 目的是得到每个单词的频率。
@@ -18,40 +21,39 @@ def freq(fruit):
     '''
 
     result = []
-    
-    fruit = fruit.lower() # 字母转小写
+    fruit = fruit.lower()  # 字母转小写
     flst = fruit.split()  # 字符串转成list
     c = collections.Counter(flst)
     result = c.most_common()
     return result
 
 
-def youdao_link(s): # 有道链接
-    link = 'http://youdao.com/w/eng/' + s + '/#keyfrom=dict2.index'# 网址
+def youdao_link(s):  # 有道链接
+    link = 'http://youdao.com/w/eng/' + s + '/#keyfrom=dict2.index'  # 网址
     return link
 
 
-def file2str(fname):#文件转字符
-    f = open(fname) #打开
-    s = f.read()    #读取
-    f.close()       #关闭
+def file2str(fname):  # 文件转字符
+    f = open(fname)  # 打开
+    s = f.read()  # 读取
+    f.close()  # 关闭
     return s
 
 
-def remove_punctuation(s): # 这里是s是形参 (parameter)。函数被调用时才给s赋值。
-    special_characters = '\_©~<=>+-/[]*&$%^@.,?!:;#()"“”—‘’{}|' # 把里面的字符都去掉
+def remove_punctuation(s):  # 这里是s是形参 (parameter)。函数被调用时才给s赋值。
+    special_characters = '\_©~<=>+-/[]*&$%^@.,?!:;#()"“”—‘’{}|'  # 把里面的字符都去掉
     for c in special_characters:
-        s = s.replace(c, ' ') # 防止出现把 apple,apple 移掉逗号后变成 appleapple 情况
+        s = s.replace(c, ' ')  # 防止出现把 apple,apple 移掉逗号后变成 appleapple 情况
     s = s.replace('--', ' ')
-    s = s.strip() # 去除前后的空格
-    
+    s = s.strip()  # 去除前后的空格
+
     if '\'' in s:
         n = len(s)
-        t = '' # 用来收集我需要保留的字符
-        for i in range(n): # 只有单引号前后都有英文字符，才保留
+        t = ''  # 用来收集我需要保留的字符
+        for i in range(n):  # 只有单引号前后都有英文字符，才保留
             if s[i] == '\'':
                 i_is_ok = i - 1 >= 0 and i + 1 < n
-                if i_is_ok and s[i-1] in string.ascii_letters and s[i+1] in string.ascii_letters:
+                if i_is_ok and s[i - 1] in string.ascii_letters and s[i + 1] in string.ascii_letters:
                     t += s[i]
             else:
                 t += s[i]
@@ -60,12 +62,12 @@ def remove_punctuation(s): # 这里是s是形参 (parameter)。函数被调用
         return s
 
 
-def sort_in_descending_order(lst):# 单词按频率降序排列
+def sort_in_descending_order(lst):  # 单词按频率降序排列
     lst2 = sorted(lst, reverse=True, key=lambda x: (x[1], x[0]))
     return lst2
 
 
-def sort_in_ascending_order(lst):# 单词按频率降序排列
+def sort_in_ascending_order(lst):  # 单词按频率降序排列
     lst2 = sorted(lst, reverse=False, key=lambda x: (x[1], x[0]))
     return lst2
 
@@ -85,39 +87,30 @@ def make_html_page(lst, fname):
     f.close()
 
 
-## main（程序入口）
+# main（程序入口）
 if __name__ == '__main__':
     num = len(sys.argv)
-
-    if num == 1: # 从键盘读入字符串
+    if num == 1:  # 从键盘读入字符串
         s = input()
-    elif num == 2: # 从文件读入字符串
+    elif num == 2:  # 从文件读入字符串
         fname = sys.argv[1]
         s = file2str(fname)
     else:
         print('I can accept at most 2 arguments.')
-        sys.exit()# 结束程序运行， 下面的代码不会被执行了。
-
-    s = remove_punctuation(s) # 这里是s是实参(argument)，里面有值
+        sys.exit()  # 结束程序运行， 下面的代码不会被执行了。
+    s = remove_punctuation(s)  # 这里是s是实参(argument)，里面有值
     L = freq(s)
     for x in sort_in_descending_order(L):
-        print('%s\t%d\t%s' % (x[0], x[1], youdao_link(x[0])))#函数导出
-
+        print('%s\t%d\t%s' % (x[0], x[1], youdao_link(x[0])))  # 函数导出
     # 把频率的结果放result.html中
-    make_html_page(sort_in_descending_order(L), 'result.html') 
-
+    make_html_page(sort_in_descending_order(L), 'result.html')
     print('\nHistory:\n')
     if os.path.exists('frequency.p'):
         d = pickle_idea.load_record('frequency.p')
     else:
         d = {}
-
     print(sort_in_descending_order(pickle_idea.dict2lst(d)))
-
     # 合并频率
     lst_history = pickle_idea.dict2lst(d)
     d = pickle_idea.merge_frequency(L, lst_history)
     pickle_idea.save_frequency_to_pickle(d, 'frequency.p')
-
-
-