登录之后更新导航

用上下文处理器app_context_processor定义函数

获取session中保存的值
返回字典

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

在父模板中更新导航，插入登录状态判断代码。、

注意用{% ... %}表示指令。
{{ }}表示变量

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>
        首页
        {% block logintitle %}{% endblock %}
        {% block registertitle %}{% endblock %}
        {% block wendatitle %}{% endblock %}
    </title>
    <script>
        function mySwitch() {
            var oBody = document.getElementById("myBody");
            var oOnoff = document.getElementById("myOnOff");
            if (oOnoff.src.match("bulbon")) {
                oOnoff.src = "http://www.runoob.com/images/pic_bulboff.gif";
                oBody.style.background = "black";
                oBody.style.color = "yellow";
            } else {
                oOnoff.src = "http://www.runoob.com/images/pic_bulbon.gif";
                oBody.style.background = "lightcyan";
                oBody.style.color = "black";
            }
        }

    </script>
    <link rel="stylesheet" type="text/css" href="../static/css/moban.css">
    {% block loginhead %}{% endblock %}
    {% block registerhead %}{% endblock %}
    {% block wendahead %}{% endblock %}

</head>
<body id="myBody" style=" padding: 0px; line-height: 1.8; color: rgb(128, 0, 0);">">
<nav>
    <img src="{{ url_for('static',filename='image/gzsxy.png') }}" alt="" width="20px">
    <script>
        document.write(Date())
    </script>
    <br>
    <a href="{{ url_for('moban') }}">首页</a>
    {% if username %}
        <a href="#">{{ username }}</a>
        <a href="{{ url_for('logout') }}">注销</a>
    {% else %}
        <a href="{{ url_for('login') }}">登录</a>
        <a href="{{ url_for('register') }}">注册</a>
    {% endif %}
    <a href="{{ url_for('wenda') }}">问答</a>
    <input type="text" placeholder="请输入关键字">
    <button type="submit">搜索</button>
</nav>
<p>{{ username }}context</p>
{% block loginbody %}{% endblock %}
{% block registerbody %}{% endblock %}
{% block wendabody %}{% endblock %}
</body>
</html>

完成注销功能。

清除session
跳转

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