Flask-Genshi¶
Flask-Genshi is an extension to Flask that allows you to easily use Genshi for templating.
Features:
- Integrates fully with Flask and works with Flask-Babel for internationalization and flatland for form processing (that is, the special support flatland has for Genshi). Other extensions such as Flask-WTF and Flask-Creole should work fine too.
- Selects configurable rendering methods from the template filename, taking care of the mimetype, doctype and XML serialization, i.e., how to close tags et cetera.
Not yet:
- Flask-Theme probably does not work with Genshi templates.
- Chameleon, not sure if it should be a separate extension or not.
Why Genshi?¶
Genshi is one of the slower templating toolkits, the idea of writing XML for templating seem horrifying and Jinja is a very nice text-based template engine. Why would Genshi possibly be interesting?
Templates are rarely the culprit in application performance. If Genshi does become a culprit you can render your templates with Chameleon which performs very well.
XML lends itself naturally to templating HTML. Genshi templates are usually much more terse and readable because Python constructs can be terminated by the XML end tags and translation strings can be extracted directly from the content of text elements.
We can also operate programmatically on template streams and run filters and transformations. We can have a layout template extract a subtitle from a page template’s title tag. Many possibilities.
Take this Jinja template:
<title>{% block title %}Page Title{% endblock %}</title> {% if show_paragraph %} <p>{% trans %}Example paragraph with {{ variable }} content{% endtrans %} {% endif %}
Compare with the Genshi version:
<title>Page Title</title> <p py:if="show_paragraph">Example paragraph with $variable content</p>
For better or worse, Python in Genshi templates is really Python. The only difference is that, like with Jinja, attribute access falls back on item access and vice versa. You need only know some basic Python and XML to write Genshi templates, and you can use existing XML tools such as support in editors.
Because invalid XML results in template errors, valid output is enforced without a need to use HTML validators. You get the benefits of XHTML with browser-friendly output, and you can swap the output format on-the-fly. You’re also writing actual XML so no need for those pesky spaces in self-closing tags: <hr/> will render to HTML as <hr> and to XHTML as <hr />.
