如何在Sphinx的html输出中包含源码行号？

extensions = [
    'sphinx.ext.autodoc',
    'sphinx.ext.viewcode',
    'sphinx.ext.githubpages',
]

html_theme = 'sphinx_rtd_theme'
html_theme_options = {
    'style_external_links': True,
    'style_nav_header_background': '#2980B9',
    'collapse_navigation': False,
    'sticky_navigation': True,
    'navigation_depth': 4,
    'includehidden': True,
    'titles_only': False,
    'display_version': True,
    'prev_next_buttons_location': 'bottom',
    'style_external_links': True,
    'vcs_pageview_mode': '',
    'style_external_links': True,
    'style_external_links_target': '_blank',
}

html_css_files = [
    'css/custom.css',
]

html_js_files = [
    'js/custom.js',
]

{% extends "!layout.html" %}

{% block extrahead %}
{{ super() }}
<link rel="stylesheet" type="text/css" href="{{ pathto('_static/css/custom.css', 1) }}" />
<script type="text/javascript" src="{{ pathto('_static/js/custom.js', 1) }}"></script>
{% endblock %}

div.highlight pre {
    counter-reset: linenumber;
}

div.highlight pre span.line:before {
    content: counter(linenumber);
    counter-increment: linenumber;
    padding-right: 0.6em;
    color: #999;
    display: inline-block;
    width: 2em;
    text-align: right;
    margin-right: 0.5em;
    border-right: 1px solid #ddd;
}

$(document).ready(function() {
    $('div.highlight').each(function() {
        var lines = $(this).find('pre').text().split('\n').length - 1;
        var $numbering = $('<ul/>').addClass('pre-numbering');
        $(this)
            .addClass('has-numbering')
            .append($numbering);
        for (i = 1; i <= lines; i++) {
            $numbering.append($('<li/>').text(i));
        }
    });
});