[Distutils] Design rationale for the egg format ?

[P.J. Eby]

At 03:59 PM 6/14/2010 +0900, David Cournapeau wrote:
>Hi,
>
>I have a few questions about the egg format implementation, and was
>hoping people who designed it could answer them:
>  - why does the filename encode some metadata (which python version if
>the package contains extensions, platform specifier) ?

As Paul mentioned, it's so that discovery can happen without needing 
anything more than a listdir().  (A legacy of eggs' origin as a 
binary plugin format.)


>  - why are the metadata split into files instead of one single 
> metadata file ?

Because that's simpler than trying to define a single universal file 
format that's forward and backward-compatible with every possible 
feature and use case.  Each use case can have an optimized file format.

It also scales better for performance when you have multiple things 
you might (or might not) be reading.  For example, since entry points 
are separate from dependencies, you you don't need to read the 
dependencies from an egg that doesn't have an entry point you're scanning for.