Flask使用Jinja2模板继承遇TemplateSyntaxError问题求助

在使用Flask的Jinja2模板继承机制时，出现以下语法错误：

jinja2.exceptions.TemplateSyntaxError: Unexpected end of template. Jinja was looking for the following tags: 'endblock'. The innermost block that needs to be closed is 'block'.

以下是涉及的代码文件：

index.html #

{% extends "layout.html" %}
{% block body %}

        <!-- Page Header-->
        <header class="masthead" style="background-image: url('{{ url_for('static',filename='assets/img/home-bg.jpg') }}')">
            <div class="container position-relative px-4 px-lg-5">
                <div class="row gx-4 gx-lg-5 justify-content-center">
                    <div class="col-md-10 col-lg-8 col-xl-7">
                        <div class="site-heading">
                            <h1>Clean Blog</h1>
                            <span class="subheading">A Blog Theme by Start Bootstrap</span>
                        </div>
                    </div>
                </div>
            </div>
        </header>
        <!-- Main Content-->
        <div class="container px-4 px-lg-5">
            <div class="row gx-4 gx-lg-5 justify-content-center">
                <div class="col-md-10 col-lg-8 col-xl-7">
                    <!-- Divider-->
                    <hr class="my-4" />
                    <!-- Pager-->
                    <div class="d-flex justify-content-end mb-4"><a class="btn btn-primary text-uppercase" href="#!">Older Posts →</a></div>
                </div>
            </div>
        </div>

{% endblock body %}

layout.html #

<!DOCTYPE html>
<html lang="en">
<head>
        <meta charset="utf-8" />
        <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no" />
        <meta name="description" content="" />
        <link href="{{ url_for('static',filename='css/styles.css') }}" rel="stylesheet" />
    </head>
    <body>
        <!-- Navigation-->
        <nav class="navbar navbar-expand-lg navbar-light" id="mainNav">
            <div class="container px-4 px-lg-5">
                <a class="navbar-brand" href="index.html">Start Bootstrap</a>
                <button class="navbar-toggler" type="button" data-bs-toggle="collapse" data-bs-target="#navbarResponsive" aria-controls="navbarResponsive" aria-expanded="false" aria-label="Toggle navigation">
                    Menu
                    <i class="fas fa-bars"></i>
                </button>
                <div class="collapse navbar-collapse" id="navbarResponsive">
                    <ul class="navbar-nav ms-auto py-4 py-lg-0">
                        <li class="nav-item"><a class="nav-link px-lg-3 py-3 py-lg-4" href="/">Home</a></li>
                        <li class="nav-item"><a class="nav-link px-lg-3 py-3 py-lg-4" href="/about">About</a></li>
                    </ul>
                </div>
            </div>
        </nav>

{% block body %} { % endblock % }

    <!-- Footer-->
        <footer class="border-top">
            <div class="container px-4 px-lg-5">
                <div class="row gx-4 gx-lg-5 justify-content-center">
                    <div class="col-md-10 col-lg-8 col-xl-7">
                        <ul class="list-inline text-center">
                            <li class="list-inline-item">
                                <a href="#!">
                                    <span class="fa-stack fa-lg">
                                        <i class="fas fa-circle fa-stack-2x"></i>
                                        <i class="fab fa-twitter fa-stack-1x fa-inverse"></i>
                                    </span>
                                </a>
                            </li>
                        </ul>
                </div>
            </div>
        </footer>
        <!-- Bootstrap core JS-->
        <script src="https://cdn.jsdelivr.net/npm/bootstrap@5.1.3/dist/js/bootstrap.bundle.min.js"></script>

    </body>
</html>

错误原因与修复方法 #

问题出在layout.html中的block闭合标签：{ % endblock % }存在多余空格，Jinja2无法识别该语法，进而判定block body未被闭合。

将该行修正为以下任意一种写法即可：

{% block body %}{% endblock %}

或者匹配block名称的规范写法：

{% block body %}{% endblock body %}

修正后Jinja2就能正确解析模板继承，错误即可解决。

内容的提问来源于stack exchange，提问作者ARHAM RUMI