登录之后更新导航

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
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

完成注销功能。

清除session

跳转

from flask import Flask, render_template, url_for, redirect, request,session
from flask_sqlalchemy import SQLAlchemy

import config

app = 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))




# 增加
# user = User(username='tan1997',password='19961021')
# db.session.add(user)
# db.session.commit()

# 查询
# user = User.query.filter(User.username == 'tan1997').first()
# print(user.username,user.password)

# 修改
# user=User.query.filter(User.username == 'tan1997').first()
# user.password=1234567
# db.session.commit()

# 删除
# user=User.query.filter(User.username == 'tan1997').first()
# db.session.delete(user)
# db.session.commit()

@app.route('/')
def myweb():
    return render_template("myweb.html")


@app.route('/login/', methods=['GET', 'POST'])
def login():
    if request.method == 'GET':
        return render_template("login.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('myweb'))
            else:
                return '密码错误'
        else:
            return '用户名不存在'



@app.route('/regist/', methods=['GET', 'POST'])
def regist():
    if request.method == 'GET':
        return render_template("regist.html")
    else:
        username = request.form.get('username')
        password = request.form.get('password')
        nickname = request.form.get('nickname')
        user = User.query.filter(User.username == username).first()
        if user:
            return ' 用户名已存在'
        else:
            user = User(username=username, password=password, nickname=nickname)
            db.session.add(user)  # 数据库，添加操作
            db.session.commit()
            return redirect(url_for('login'))

@app.context_processor
def mycontext():
    username = session.get('user')
    if username:
        return {'username': username}
    else:
        return {}

@app.route("/logout/")
def logout():
    session.clear()
    return redirect(url_for('myweb'))

@app.route('/question/')
def question():
    return render_template("question.html")


if __name__ == '__main__':
    app.run(debug=True)

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8"/>
    <title>主页 {% block logintitle %}
    {% endblock %}
        {% block registtitle %}
        {% endblock %}
        {% block questiontitle %}
        {% endblock %}
    </title>

    <link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet">
    <link rel="stylesheet" type="text/css" href="{{ url_for('static',filename='css/myweb.css') }}">
    <script src="{{ url_for('static',filename='js/switch.js') }}"></script>
    {% block loginhead %}
    {% endblock %}
    {% block registhead %}
    {% endblock %}
    {% block questionhead %}
    {% endblock %}
</head>

<body id="myBody" style="background-image: url(../static/img/demo-1-bg.jpg)">

<ul>
    <li><img class="ico" src="../static/img/ico.jpg" alt="" style="margin-top: 12px"></li>
    <li><a href="{{ url_for('myweb') }}">首页</a></li>
    <li><input type="text" class="form-control"  placeholder="Search" style="margin-top: 8px" ></li>
    <li><button type="submit" class="btn btn-default" style="margin-top: 8px">搜索</button></li>
    <li><a href="{{ url_for('question') }}">提问</a></li>
    {% if username %}
        <li><a href="#">{{ username }}</a></li>
        <li><a href="{{ url_for('logout') }}">注销</a></li>
    {% else %}
        <li style="float:right"><a href="{{ url_for('login') }}">登陆</a></li>
        <li style="float:right"><a href="{{ url_for('regist') }}">注册</a></li>
    {% endif %}
    <li style="float: right"><img id="myOnOff" onclick="mySwitch()" src="http://www.runoob.com/images/pic_bulbon.gif" class="bulb"></li>
</ul>
<footer>
    <div class="footer_box">
        <p>Posted by: W3School</p>
        <p>Contact information: <a href="mailto:someone@example.com">someone@example.com</a>.</p>
    </div>
</footer>
{% block loginbody %}  {% endblock %}
{% block registbody %}  {% endblock %}
{% block questiontbody %} {% endblock %}
</body>
</html>