我简单修改了一下 上下页的代码，逻辑可能更清晰一些

detail.html

<nav aria-label="...">
    <ul class="pager">
        {% if previous_article %}
        <li><a href="/blog/detail/{{previous_article.article_id}}">上一篇：{{previous_article.title}}</a></li>
        {% endif %}
        {% if next_article %}
        <li><a href="/blog/detail/{{next_article.article_id}}">下一篇：{{next_article.title}}</a></li>
        {% endif %}
    </ul>
</nav>

views.py

def get_detail_page(request, article_id):
    curr_article = Article.objects.filter(article_id=article_id)[0]
    previous_article = Article.objects.filter(article_id__lt=article_id).last()
    next_article = Article.objects.filter(article_id__gt=article_id).first()
    section_list = curr_article.content.split('\n')
    return render(request, 'blog/detail.html', {
        'curr_article': curr_article,
        'section_list': section_list,
        'previous_article': previous_article,
        'next_article': next_article,
    })