Use a better variable name (fix session variable name error).

app/templates/userpage_get.html

@@ -28,7 +28,13 @@
     </p>
     {{ flashed_messages|safe }}
 
-    <p><a class="btn btn-success" href="/{{ username }}/reset" role="button"> 下一篇 Next Article </a></p>
+    <a class="btn btn-success" href="/{{ username }}/reset" role="button"> 下一篇 Next Article </a>    
+    {% if session.get('articleID') != session.get('old_articleID') %}
+        {% if session.get('old_articleID') != None %}
+            <a class="btn btn-success" href="/{{ username }}/back" role="button"> 上一篇 Previous Article </a>
+        {% endif%}
+    {% endif %}
+
     <p><b>阅读文章并回答问题</b></p>
     <div id="text-content">{{ today_article|safe }}</div>
 

app/user_service.py

@@ -29,12 +29,25 @@ def user_reset(username):
     :param username: 用户名
     :return: 返回页面内容
     '''
+    session['old_articleID'] = session.get('articleID')
     if request.method == 'GET':
         session['articleID'] = None
         return redirect(url_for('user_bp.userpage', username=username))
     else:
         return 'Under construction'
 
+@userService.route("/<username>/back", methods=['GET'])
+def user_back(username):
+    '''
+    用户界面
+    :param username: 用户名
+    :return: 返回页面内容
+    '''
+    if request.method == 'GET':
+        session['articleID'] = session.get('old_articleID')
+        return redirect(url_for('user_bp.userpage', username=username))
+
+
 
 @userService.route("/<username>/<word>/unfamiliar", methods=['GET', 'POST'])
 def unfamiliar(username, word):