[Distutils] Seeking the Essence of the Concept of an Egg
Phillip J. Eby
pje at telecommunity.com
Thu Feb 28 16:48:41 CET 2008
At 04:46 AM 2/28/2008 -0600, Jeff Rush wrote:
>In preparing for a tutorial on Python eggs, I'm wrestling with the
>*precise* definition of a "Python egg". It appears to be a slippery
>term from the various documentation:
> "There are several binary formats that embody eggs, but the most
> common is '.egg' zipfile format, because it's a convenient one
> for distributing projects. All of the formats support including
> package-specific data, project-wide metadata, C extensions, and
> Python code."
>Ok, so what binary formats -other than- .egg files are actually
>eggs? I figure RPMs, .debs, etc. are eggs, as long as they have an
>EGG-INFO subdirectory and conform to certain basic structural rules.
No - they're not. They *contain* eggs, they aren't eggs themselves.
> "Eggs are pluggable distributions in one of the three formats
> currently supported by ``pkg_resources``. There are built
> eggs, development eggs, and egg links."
>Hmmm, so it's not just binary distributions that can be eggs, but
>also egg-links and development eggs. The concept of a "built egg"
>egg still includes an RPM or .deb though.
Development eggs are .egg-info eggs. This definition *is* a bit
slippery though, in that an egg link isn't "really" an egg, except in
the sense that a symlink to a directory is a directory. :)
If you want a solid definition, I'd say that built eggs (.egg file or
directory) and development eggs (.egg-info eggs) are the only "real"
eggs, as they are directly importable (as described below).
> "Python Eggs are the preferred binary distribution format for
> EasyInstall, because they are cross-platform (for "pure"
> packages), directly importable, and contain project metadata
> including scripts and information about the project's
> dependencies. They can be simply downloaded and added to
> sys.path directly, or they can be placed in a directory on
> sys.path and then automatically discovered by the egg
> runtime system."
>Well drat, so RPMs and .debs are -not- eggs, because you don't just
>place them on sys.path directly to use them. Egg-links don't quite
>fit that definition either, unless you look at them funny. So what
>-other- binary format could that first paragraph be talking about
>that can be dropped onto sys.path and be picked up by Python?
There isn't one now - it was phrased that way to leave open future
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