I'm writing about upgrading the "stable" version of yt to the a new naming scheme. Before I say anything else, let me start out and say that because of the potentially disruptive nature of this change, you should feel free to either refrain from upgrading your yt installation or emailing me directly (off-list) to get assistance with the upgrade process.
We're planning on moving the "stable" version of the code to be the 2.0 API in the next few weeks, where we have removed the names lagos, raven, etc, in favor of more informative names like visualization, data_objects, and so on. This change was described by Jeff in an email to the list a few months ago, which has been summarized here: http://yt.enzotools.org/wiki/yt-2.0 . I would like to encourage you to upgrade now, rather than later, so that we can try to work out any potential issues in advance of the upgrade of the title "stable." Documentation is almost completely update and will be done before the "stable" branch reflects the new API.
I've updated the homepage to now encourage new users to use the development version, which features the new module names, etc. If you would like to continue using the version you are on, you should be able to continue to do so by not upgrading.
If you would like to upgrade, a new installation may be the easiest way, or otherwise you should be able to get the directory name of the current yt installation from "yt instinfo" and execute: "hg pull ; hg up -C yt ; hg purge ; python2.6 setup.py develop" in that directory.
I'm working on updating the documentation to reflect this, but the upshot of all of the API changes is that *everything* that is needed to do all the standard analysis tasks is still available just with the command:
from yt.mods import *
If you are executing anything that requires directly calling "lagos" or "raven", please contact me directly (off-list) and I will assist you with the upgrade of your scripts. If you think it's a relatively broad concern about module naming and so on, feel free to email the list.
Thanks very much,