Error on accessing page.meta.foo

[lakonis]

Hello,
I am trying to add a few additional <meta> from the main.html template through custom_theme. I succeeded to do so, but I cannot use page.meta correctly.

{{ page.meta }} returns no error and it lists all pairs "key-value" as 'key' : 'value', but when calling {{ page.meta.foo }}, I get this error on build or serve:

  File "~/.local/lib/python3.8/site-packages/tornado/ioloop.py", line 905, in _run
    return self.callback()
  File "~/.local/lib/python3.8/site-packages/livereload/handlers.py", line 69, in poll_tasks
    filepath, delay = cls.watcher.examine()
  File "~/.local/lib/python3.8/site-packages/livereload/watcher.py", line 119, in examine
    func()
  File "~/.local/lib/python3.8/site-packages/mkdocs/commands/serve.py", line 136, in builder
    build(config, live_server=live_server, dirty=dirty)
  File "~/.local/lib/python3.8/site-packages/mkdocs/commands/build.py", line 285, in build
    _build_theme_template(template, env, files, config, nav)
  File "~/.local/lib/python3.8/site-packages/mkdocs/commands/build.py", line 108, in _build_theme_template
    output = _build_template(template_name, template, files, config, nav)
  File "~/.local/lib/python3.8/site-packages/mkdocs/commands/build.py", line 87, in _build_template
    output = template.render(context)
  File "~/.local/lib/python3.8/site-packages/jinja2/environment.py", line 1090, in render
    self.environment.handle_exception()
  File "~/.local/lib/python3.8/site-packages/jinja2/environment.py", line 832, in handle_exception
    reraise(*rewrite_traceback_stack(source=source))
  File "~/.local/lib/python3.8/site-packages/jinja2/_compat.py", line 28, in reraise
    raise value.with_traceback(tb)
  File "~/.local/lib/python3.8/site-packages/mkdocs/themes/readthedocs/search.html", line 1, in top-level template code
    {% extends "main.html" %}
  File "~/githn/HUMANUM/documentation/custom_theme/main.html", line 2, in top-level template code
    {% extends "base.html" %}
  File "~/.local/lib/python3.8/site-packages/mkdocs/themes/readthedocs/base.html", line 5, in top-level template code
    {%- block site_meta %}
  File "~/githn/HUMANUM/documentation/custom_theme/main.html", line 26, in block "site_meta"
    <!-- une tentative {{ page.meta.description }} -->
  File "~/.local/lib/python3.8/site-packages/jinja2/environment.py", line 471, in getattr
    return getattr(obj, attribute)
jinja2.exceptions.UndefinedError: 'None' has no attribute 'meta'

What do I do wrong ?
Thank you !

[waylan]

According to the traceback, the template being rendered when that error occurs is readthedocs/search.html. which is a static template. As it is not a "page", it does not have the page variable defined. Notice that the error suggests that page is None. To avoid the error, you need to wrap the call to page in an if statement:

{% if page %}{{ page.meta.description }}{% endif %}

That way, the description will be included for "pages", but will be blank for static templates and other non-page documents.

In fact, if you look at the theme's template, you will notice that every reference to page is wrapped in {% if page %} for this very reason.

[lakonis]

Thank you very much ! I suggest to precise that in the doc, as it is not clearly stated when reading custom_theme and page.meta.

[waylan]

The documentation for page states:

In templates which are not rendered from a Markdown source file, the page variable is None. In templates which are rendered from a Markdown source file, the page variable contains a page object.

Note sure how we can make it any more clear. Adding the page information to page.meta would be redundant. The same would apply to every attribute of page, so we comment on the issue at the page level.

[lakonis]

Sorry, I don't understand. My page sources are markdown. The template is in html, extending main.html. Should I understand that my pages are not pages anymore because I extended the template ?

[waylan]

All Markdown based documents are always "pages". Any document which was generated by MkDocs but does not come from a Markdown file is not a "page." The specific document you encountered in your error is search.html which is where search results are displayed in the readthedocs theme. There is no corresponding Markdown file for that document. However, we want the document to look like the rest of the pages with the same navigation, etc, so it is run through the template just like a Markdown based page. The same would apply to any other static_templates and extra_templates.

Therefore, your templates must account for both Markdown based pages and non-markdown based documents.

[lakonis]

Very clear thank you !

[waylan]

I am converting this to a discussion, as it is a support request, not a bug report or feature request.

[lakonis]

Then, what is not a page ? (sorry if naive question)