Ophelia – build a web site from templates with zero code repetition
Ophelia creates XHTML pages from templates written in TAL, the Zope Template Attribute Language. It is designed to reduce code repetition to zero.
Ophelia is a WSGI application. The package includes a wsgiref-based server configured to run Ophelia as well as an application factory for use with paster.
The package requires Python 2.6 or 2.7.
Documentation files cited below can be found inside the package directory, along with a number of doctests for the modules.
After you installed Ophelia and wrote some templates, how can you make it render web pages?
- Use Ophelia as a WSGI application
- Ophelia defines an application class compliant with the WSGI standard, PEP 333: ophelia.wsgi.Application. You can either try it by running Ophelia's own wsgiref-based HTTP server or run it by any WSGI server you might care to use.
- Try the wsgiref-based server that comes with Ophelia
A rather simplistic and non-production-ready wsgiref-based server set up to use the provided WSGI application is installed as the ophelia-wsgiref executable. Its script entry point is ophelia.wsgi.wsgiref_server.
The script provides some usage instructions when called with the --help option. It reads a configuration file; see CONFIGURATION.txt for details.
- Use paster to plug the application into a WSGI server
- Ophelia provides a paste.app_factory#main entry point at ophelia.wsgi.Application.paste_app_factory. This can be used to run Ophelia inside any WSGI server that can read paste "ini" files. See CONFIGURATION.txt for an example.
What kind of sites is Ophelia good for?
Consider Ophelia as SSI on drugs. It's not fundamentally different, just a lot friendlier and more capable.
Use Ophelia for sites where you basically write your HTML yourself, except that you need write the recurring stuff only once. Reducing repetition to zero comes at a price: your site must follow a pattern for Ophelia to combine your templates the right way.
Consider your site's layout to be hierarchical: there's a common look to all your pages, sections have certain characteristics, and each page has unique content. It's crucial to Ophelia that this hierarchy reflect in the file system organization of your documents; how templates combine is deduced from their places in the hierarchy of directories.
Ophelia makes the Python language available for including dynamic content. Each template file may include a Python script. Python scripts and templates contributing to a page share a common set of variables to modify and use.
Ophelia's content model is very simple and works best if each content object you publish is its own view: the page it is represented on. If you get content from external resources anyway (e.g. a database or a version control repository), it's still OK to use Ophelia even with multiple views per content object as long as an object's views don't depend on the object's type or even the object itself.
Trying to use Ophelia on a more complex site will lead to an ugly entanglement of logic and presentation. Don't use Ophelia for sites that are actually web interfaces to applications, content management systems and the like.
How Ophelia works
For each request, Ophelia looks for a number of template files. It takes one file named "__init__" from each directory on the path from the site root to the page, and a final one for the page itself. The request is served by Ophelia if that final template is found.
When building the page, the page's template is evaluated and its content stored in what is called the inner slot. Then each template on the way back from the page to the root is evaluated in turn and may include the current content of the inner slot. The result is stored in the inner slot after each step.
The result of processing the root template is served as the page.
Each template file may start with a Python script. In that case, the script is separated from the template by the first occurrence of an "<?xml?>" tag on a line of its own (except for whitespace left or right). If the template file contains only a Python script but not actually a template, put "<?xml?>" in its last line.
Python scripts are executed in order while traversing from the site root to the page. They are run in the same namespace of variables that is later used as the evaluation context of the templates. Variables that are set by a Python script may be used and modified by any scripts run later, as well as by TALES expressions used in the templates.
The namespace is initialized by Ophelia with a single variable, __request__, that references the request object. Thus, scripts have access to request details and traversal internals. In addition to setting variables, scripts may also import modules, define functions, access the file system, and generally do anything a Python program can do.
Documents on disk
In order to mix such content into the URL space of an Ophelia-generated site, the template hierarchy must omit the relevant paths and a second directory hierarchy which directly corresponds to the URL-space needs to contain the documents to be delivered from disk. If Ophelia then finds that it cannot serve a request using the templates, it will fall back to the on-disk documents. Only if the latter do not include a file corresponding to the requested URL will a "404 Not found" error response be sent.
How Ophelia behaves
URL canonicalization and redirection
If Ophelia encounters a URL that corresponds to a directory it behaves similarly to Apache in its default configuration: If the URL doesn't end with a slash, it will redirect the browser to add the slash. If the slash is there, it will try to find a template named index.html by default, and render it as the directory "index".
Depending on configuration, explicit requests for directory index pages may be redirected to bare directory URLs without the final path segment. This would turn <http://www.example.com/index.html> into <http://www.example.com/>.
Additionally, Ophelia canonicalizes URLs containing path segments "." and ".." according to RFC 3986 on generic URI syntax, and removes empty path segments which are not at the end of the path. If the URL is changed by these rules, Ophelia redirects the browser accordingly.
Languages and APIs used in templates and scripts
For the Python language, see <http://docs.python.org/>.
For the Template attribute language, see <http://wiki.zope.org/ZPT/TAL>.
For WSGI, the web server gateway interface, see <http://www.python.org/dev/peps/pep-0333/>.
For the Ophelia API and predefined script and template variables, see API.txt.