enstaller 4.6.3

Install and managing tool for egg-based packages

The Enstaller (version 4) project is a package management and installation tool for egg-based Python distributions.

Enstaller consists of the sub-packages enstaller (package management tool) and egginst (package (un)installation tool). We find the clean separation into these two tasks, each of which has a well-defined scope, extremely useful.

enstaller:

enstaller is a management tool for egginst-based installs. The CLI, called enpkg, calls out to egginst to do the actual installation. 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.

egginst:

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 shorter python path and faster import times (which seems to make the biggest difference for namespace packages). egginst knows about the eggs the people from Enthought use. It can install shared libraries, change binary headers, etc.—things which would require special post-install scripts if easy_install installed them.

The egg format:

The Enstaller egg format deals with two aspects: the actual install (egginst), and 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 is a brain dead low-level tool, it will even install an egg without an ‘EGG-INFO’ directory. But more importantly, egginst installs ordinary setuptools eggs just fine. Within the ‘EGG-INFO/’ namespace are special archives that 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 metadata file with the archive name ‘EGG-INFO/spec/depend’. 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.

Egg file name format:

Eggs follow the following naming convention:

<name>-<version>-<build>.egg

<name>

The package name, which may contain the following characters: Letters (both lower or uppercase), digits, underscore ‘_’ and a dot ‘.’

<version>

The version number, which is restricted to containing the same characters as the package name, and which should follow PEP 386.

<build>

The build number, which may only contains digits (with no leading zeros). This number is used to distinguish between different eggs which were build from the same project source. Having different build numbers becomes necessary when, for example: eggs are build for different Python versions, a build bug is fixed, a patch is applied to the source, etc.

The regular expression for a valid egg file name is:

r'([\w.]+)-([\w.]+)-(\d+)\.egg$'

The metadata format:

Build numbers are a way to differentiate eggs which have the same name and version but different dependencies. The platform and architecture dependencies of a distribution (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.

Installation:

The preferred and easiest way to install Enstaller is from the executable egg, i.e. the Enstaller egg contains a bash header and on Unix systems you can download the egg and type:

$ bash enstaller-4.6.1-1.egg
Bootstrapping: ...
283 KB [.................................................................]

Once Enstaller is installed, it can update itself. Note that, as Enstaller is the install tool for the Enthought Python Distribution (EPD), all EPD installers already include Enstaller.