The Enstaller (version 4) project is a managing and install tool for egg-based Python distributions.
Enstaller consists of the sub-packages enstaller and egginst:
enstaller is a managing tool for egginst-based installs, and the CLI is called enpkg which calls out to egginst to do the actual install. enpkg can access distributions from local and HTTP repositories, which are pre-indexed. The point of the index file (index-depend.bz2) is that enpkg can download this file at the beginning of an install session and resolve dependencies prior to downloading the actual files. The CLI called 'index-tool' provides tools to create the index file in an egg directory which can then be served over HTTP.
egginst is the underlying tool for installing and uninstalling eggs. The tool is brain dead in the sense that it does not care if the eggs it installs are for the correct platform, it's dependencies got installed, another package needs to be uninstalled prior to the install, and so on. Those tasks are responsibilities of a package manager, and are outside the scope of egginst.
egginst installs modules and packages directly into site-packages, i.e. no .egg directories are created, hence there is no extra .pth-file which results in a sorter python path and faster import times (which seems to have the biggest advantage for namespace packages). egginst knows about the eggs the people from Enthought use. It can install shared libraries, change binary headers, etc., things which require special post install scripts if (Enstaller) easy_install installs them.
The egg format:
The Enstaller egg format deals with two aspects: the actual install (egginst), and the distribution management (enpkg). As far as egginst is concerned, the format is an extension of the setuptools egg format, i.e. all archive files, except the ones starting with 'EGG-INFO/' are installed into the site-packages directory. In fact, since egginst a brain dead low-level tool, it will even install an egg without an 'EGG-INFO' directory. But more importantly, egginst installs ordinary setuptools just fine. Within the 'EGG-INFO/' namespace are special archives which egginst is looking for to install files, as well as symbolic links, into locations other than site-packages, and post install (and pre uninstall) scripts it can run.
As far as enpkg is concerned, eggs should contain a meta-data file with the archive name 'EGG-INFO/spec/depend'. The the index file (index-depend.bz2) is essentially a compressed concatenation of the 'EGG-INFO/spec/depend' files for all eggs in a directory/repository.
The metadata format:
Build numbers are a way to differentiate eggs which have the have the same name and version, but different dependencies. The platform and architecture dependencies of a distributions (or egg) is most easily differentiated by putting them into different directories. This leaves us with the Python dependency and other egg dependencies to put into the build number. A dependencies specification data file is contained inside the egg itself, that is in the archive EGG-INFO/spec/depend, and the md5sum and filesize is prepended to the data when the index-depend.bz2 is created.
At PyCon 2010 in Atlanta, the author of Enstaller gave a talk with the
subject title "How does Enthought distribute packages?".
Here are the slides: talk_108.pdf