[Distutils] Twisted plugin system and Python packaging

[P.J. Eby]

At 04:20 PM 9/21/2011 +0200, Tristan Seligmann wrote:
>If you include "twisted.plugins" in your setup.py, then this works 
>fine with distutils "setup.py install" as well as "pip install"; 
>setuptools "setup.py install" will install everything into an egg, 
>which will also work due to the way __path__ is set. However, since 
>"twisted" ends up in top_files.txt in the egg-info, "pip uninstall" 
>will blow away your whole Twisted install when uninstalling a 
>project shipping Twisted plugins that was installed with "pip install".

This really sounds like a bug in pip; top_level.txt is not a 
replacement for a proper uninstall log.

>So, how should Twisted and Twisted-related projects be packaged in 
>order to avoid these issues? Please bear in mind that the current 
>plugin system in Twisted was first introduced around March 2005 
>(replacing the even older plugin system in use at the time, I 
>believe), thus there are quite a number of users relying on this 
>code; any changes would need to be backwards-compatible to avoid 
>causing problems for all of the existing projects and users relying 
>on the functionality.

I think you've answered your own question here: there *isn't* any way 
to package Twisted-related projects in a way that avoids the issue, 
due to the bug in pip.  It's not Twisted's fault that pip takes shortcuts here.