父文件：index.html
<!DOCTYPE html>
<html lang="en">
<head>
<title>{% block title %}Index{% endblock %}</title>
<meta charset="utf-8">
<script src="https://cdn.bootcss.com/jquery/1.10.2/jquery.min.js"></script>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="../static/css/index.css">
<script src="static/js/index.js"></script>
<link rel="stylesheet" href="https://cdn.bootcss.com/bootstrap/4.1.0/css/bootstrap.min.css">
<script src="https://cdn.bootcss.com/jquery/3.2.1/jquery.min.js"></script>
<script src="https://cdn.bootcss.com/popper.js/1.12.5/umd/popper.min.js"></script>
<script src="https://cdn.bootcss.com/bootstrap/4.1.0/js/bootstrap.min.js"></script>
</head>
<body>
<nav class="navbar navbar-expand-sm bg-dark navbar-dark">
<!--导航栏-->
<a class="navbar-brand" href="/">
{% block ico %}<img src="/static/images/ppl.jpg" alt="logo" style="50px;"> {% endblock %}
</a>
<!--<h2>胶囊</h2>-->
<!--<p>胶囊导航:</p>-->
<ul class="nav nav-pills">
<li class="nav-item">
<a class="nav-link" href="/">首页</a>
</li>
<li class="nav-item">
<a class="nav-link" href="/insert/" id="insert">insertPerson</a>
</li>
<li class="nav-item">
<a class="nav-link" href="/get1/">addAccount</a>
</li>
<li class="nav-item">
<a class="nav-link" href="/search1/">SearchPerson</a>
</li>
<li class="nav-item">
<a class="nav-link disabled" href="#">SearchPerson</a>
</li>
<li class="nav-item dropdown">
<a class="nav-link dropdown-toggle" data-toggle="dropdown" href="#">注册/登录</a>
<div class="dropdown-menu">
<a class="dropdown-item" href="#">注册</a>
<a class="dropdown-item" href="#">登录</a>
<a class="dropdown-item" href="#">登出</a></div>
</li>
</ul>
</nav>
{% block index %}
<br>
<div id="demo" class="carousel slide" data-ride="carousel">
<!-- 指示符 -->
<ul class="carousel-indicators">
<li data-target="#demo" data-slide-to="0" class="active"></li>
<li data-target="#demo" data-slide-to="1"></li>
<li data-target="#demo" data-slide-to="2"></li>
</ul>
<!-- 轮播图片 -->
<div class="carousel-inner" >
<div class="carousel-item active">
<img src="http://static.runoob.com/images/mix/img_fjords_wide.jpg" style="100%">
</div>
<div class="carousel-item">
<img src="http://static.runoob.com/images/mix/img_nature_wide.jpg" style="100%">
</div>
<div class="carousel-item">
<img src="http://static.runoob.com/images/mix/img_mountains_wide.jpg" style="100%">
</div>
</div>
<!-- 左右切换按钮 -->
<a class="carousel-control-prev" href="#demo" data-slide="prev">
<span class="carousel-control-prev-icon"></span>
</a>
<a class="carousel-control-next" href="#demo" data-slide="next">
<span class="carousel-control-next-icon"></span>
</a>
</div>
<div class="foot-box"></div>
{% endblock %}
<!--实现鼠标滑过导航栏增加active类属性-->
<script>
$(document).ready(function(){
$('.nav-link').hover(
function(){
$(this).addClass('active');
},
function(){
$(this).removeClass('active');
}
);
});
</script>
</body>
</html>
子文件-继承自index.html
{% extends "index.html" %}
{% block title %}Insert{% endblock %}
{% block index %}
<!--<form action="/do/" method="post">-->
<!--姓名：<input type="text" name="username"><br>-->
<!--年龄：<input type="text" name="userage"><br>-->
<!--<input type="reset">-->
<!--<button type="submit">提交</button>-->
<!--</form>-->
<div class="container">
<br>
<a href="#demo" class="btn btn-primary" data-toggle="collapse">插入新人信息</a>
<div id="demo" class="collapse">
<form action="/do/" method="post">
<div class="form-group">
<label for="user">Username:</label>
<input type="text" class="form-control" id="user" name="username" placeholder="Enter Username">
</div>
<div class="form-group">
<label for="age">Userage:</label>
<input type="password" class="form-control" id="age" name="userage" placeholder="Enter Userage">
</div>
<div class="form-check">
<label class="form-check-label">
<input class="form-check-input" type="checkbox"> Remember me
</label>
</div>
<button type="submit" class="btn btn-primary">Submit</button>
</form>
</div>
</div>
{% endblock %}
注意！！！
在index.html文件中的
{% block ico %}<img src="/static/images/ppl.jpg" alt="logo" style="50px;"> {% endblock %}
中
src="/static/images/ppl.jpg" 和 src="static/images/ppl.jpg" 完全不一样的效果，前者被继承后子页面的logo可正常显示，后者则会出现图片无法加载的问题。
因为在settings中我们已经设置了静态文件收集路径，在base模板中索引静态文件的时候需要从static根路径下进行索引，故需要加"/"，此坑难发现，还需多学习。