Albatross 1.30 released

Andrew McNamara andrewm at
Tue May 31 09:40:50 CEST 2005


Albatross is a small toolkit for developing highly stateful web

The toolkit has been designed to take a lot of the pain out of
constructing intranet applications although you can also use Albatross
for deploying publicly accessed web applications.

In slightly more than 4500 lines of Python (according to pycount) you
get the following:

  * An extensible HTML templating system similar to DTML including tags for:
    - Conditional processing.
    - Macro definition and expansion.
    - Sequence iteration and pagination.
    - Tree browsing.
    - Lookup tables to translate Python values to arbitrary template

  * Application classes which offer the following features:
    - Optional server side or browser side sessions.
    - The ability to place Python code for each page in a dynamically
      loaded module, or to place all page processing code in a single

  * The ability to deploy applications as CGI, FastCGI, mod_python or
    a pure python HTTP server by changing less than 10 lines of code.

The toolkit application functionality is defined by a collection of
fine grained mixin classes.  Nine different application types and six
different execution contexts are prepackaged, you are able to define
your own drop in replacements for any of the mixins to alter any
aspect of the toolkit semantics.

Application deployment is controlled by your choice of either cgi,
FastCGI, mod_python, or BaseHTTPServer Request class.  It should be
possible to develop a Request class for Medusa or Twisted to allow
applications to be deployed on those platforms with minimal changes.

Albatross comes with over 170 pages of documentation.  HTML, PDF and
PostScript formatted documentation is available from the toolkit

The toolkit homepage:

The Albatross mailing list subscription and archives:


  * Any HTML tag can now be prefixed with "al-" allowing any attribute to be
    the result of python evaluation. For example:

      <al-td colspanexpr="i.span()"> could produce <td colspan="3">


      <al-input name="abc.value" disabledbool="abc.isdisabled()">
      could produce <input name="abc.value" disabled>

  * Since macros and lookups are an application global resource, they can
    only be defined once per application, however this was not previously
    checked. Redefinition of macros or lookups will now result in an
    ApplicationError exception.

  * an in-line version of the <al-lookup> tag has been introduced, which is
    expanded in place if the tag has an expr= attribute.

  * a new <al-require> tag has been added to allow templates to assert that
    specific Albatross features are available, or templating scheme version
    number is high enough.

  * "Cache-Control: no-cache" is now set in addition to "Pragma: no-cache"
    - the former is defined for HTTP/1.1, the later for HTTP/1.0.

  * Simplified session cookie handling.


  * FastCGI apps were not being explicitly finalised, relying
    instead on their object destructor, with the result that writing
    application output (or errors) would be indefinitely deferred if
    object cycles existed. We now call "fcgi.Finish()" from the fcgiapp
    Request.return_code() method.

  * When handling exceptions, the traceback is now explicitly deleted
    from the local namespace to prevent cycles (otherwise the garbage
    collection of other objects in the local namespace will be delayed).

  * Two fixes to the <al-select> tag: the albatross-specific "list"
    attribute was leaking into resulting markup, and the use of the "expr"
    attribute would result in invalid markup being emitted.

  * Thanks to Robert Fendt for picking this up: the Albatross-generated
    hidden field input element must not appear naked inside a form
    element for strict HTML conformance.  The solution is to wrap the
    input elements in div.

  * BranchingSession sessions could not be "deleted" - the solution is
    to add a dummy "session" shared by all branches, which is deleted
    when one branch "logs out".

Andrew McNamara, Senior Developer, Object Craft

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