1. 用上下文处理器app_context_processor定义函数
   1. 获取session中保存的值
   2. 返回字典
2. 在父模板中更新导航，插入登录状态判断代码。
   1. 注意用{% ... %}表示指令。
   2. {
      { }}表示变量
3. 完成注销功能。
   1. 清除session
   2. 跳转

index.py

import configfrom flask import Flask, render_template, url_for, redirect, request,sessionfrom flask_sqlalchemy import SQLAlchemyapp = Flask(__name__)app.config.from_object(config)db = SQLAlchemy(app)class User(db.Model):    __tablename__ = 'user'    id = db.Column(db.Integer, primary_key=True, autoincrement=True)    username = db.Column(db.String(20), nullable=False)    password = db.Column(db.String(20), nullable=False)    nickname = db.Column(db.String(20))db.create_all()@app.route('/')def shouye():    return render_template('text.html')@app.route('/zhuce',methods=['GET','POST'])def zhuce():    if request.method == 'GET':        return render_template('zhuce.html')    else:        username = request.form.get('username')        password = request.form.get('password')        nickname = request.form.get('nickname')        user1 = User.query.filter(User.username == username).first()    if user1:        return 'username existed'    else:        user1 = User(username=username, password=password, nickname=nickname)        db.session.add(user1)        db.session.commit()        return redirect(url_for('denglu'))@app.route('/denglu',methods=['GET','POST'])def denglu():    if request.method == 'GET':        return render_template('denglu.html')    else:        username = request.form.get('username')        password = request.form.get('password')        user=User.query.filter(User.username == username).first()    if user:        if user.password == password:            session['user'] = username            session.permanent = True            return redirect(url_for('shouye'))        else:            return 'password error'    else:        return 'username is not existed'@app.route('/logout/')def logout():    session.clear()    return redirect(url_for('shouye'))@app.route('/neirong')def fankui():    return render_template('fankui.html')@app.context_processordef mycontext():    usern=session.get('user')    if usern:        return {
   'username':usern}    else:        return {}if __name__ == '__main__':    app.run(debug='True')

denglu.html

    {% extends "text.html" %}    
             
         
      {% block js %}  {% endblock %}{% block denglu %}    
     
      
    
       
        
        
            
         
          wgd
         
            
         
                
          
用户登录
                
          
 
           
            
           
 
            
          
                
          
  
                
          
 
           
            
           
 
            
          
                
          
  
                
          
 
           
 
            登录 
           
 
           
 
            注册 |
             忘记密码？ 
           
 
          
            
         
        
        
    
       
      
     
{% endblock %}

父模板text.hrml

    
              
         {% block js %}{% endblock %}
     
  
        
      
    
       
      
        
        首页 (current)      
      
        
        动画      
      
        
        音乐      
      
        
        游戏      
    
        
        
                 
         搜索    
        
       
  
      
    
      
               {% if username%}            
       {
   { username }}               
       注销        {% else %}                
       登陆                   
       注册        {% endif %}    
      
     
{% block denglu %}{% endblock %}{% block zhuce %}{% endblock %}{% block fankui %}{% endblock %}
     
    
      
        
       内容发布    
      
     

shouye.html

    {% extends "text.html" %}    
                 {% block shouye %}{% endblock %}

实验截图