Poaching (Patching) Eggs

The term “egg” as used in the Python community seems so whimsical.  It deserves lots of puns.  A couple of weeks ago, I made a little utility for myself that takes all the eggs from an egg farm produced by zc.buildout and makes a single directory tree full of Python packages and modules.  I called it Omelette.  Get it?  Ha!  (I can hear chickens groaning already…)  The surprising thing about Omelette is it typically finishes in less than 1 second, even with dozens of eggs and thousands of modules.  It mostly produces symlinks, but it also unpacks zip files.  I plan to share it, but I don’t know when I’ll get around to packaging it.

Anyway, I want to talk about poaching patching eggs.  As systems grow in complexity, patching becomes more important.  Linux distributors, for example, solve a really complex problem, and their solution is to patch nearly every package.  If they didn’t, installed systems would be an unstable and unglued mess.  I imagine distributors’ patches usually reach upstream maintainers, but I also imagine it often takes months or years for those patches to trickle into a stable release of each package.

I really want to find a good way to integrate patching into the Python egg installation process.  I want to be able to say, in package metadata, that my package requires ZODB with a certain patch.  That patch would take the form of a diff file that might be downloaded from the Web.  I also want to be able to say that another package requires ZODB with a different patch, and assuming those patches have no conflicts, I want the Python package installation system to install ZODB with both patches.  Moreover, I want other buildouts to use ZODB without patches, even though I have a centralized cache of eggs in my ~/.buildout directory.

So let’s say my Python package installation system is zc.buildout, setuptools, and distutils.  Which layer should be modified to support patching?  I don’t think the need for automated patching arises until you’re combining a lot of packages, so it would seem most natural to put patching in zc.buildout. I can imagine a build.cfg like this:

ZODB3=3.8.1 +poll-invalidations


I wonder how difficult it would be to achieve that.  Some modification of setuptools might be required.  Alternatively, can Paver patch eggs?  I suspect Paver is not very good at patching eggs either.

5 thoughts on “Poaching (Patching) Eggs”

  1. I’m inclined to approach this slightly differently. First, there’s no good way to deal with branches with our current systems. There’s a sense of a single timeline of the package, and you either have a newer version or an older version, you can’t have a sideways version. So first I’d like a clear way to talk about a sideways version.

    From there, maybe the sideways version could be maintained as a patch with a simple stub of a setup.py. The setup.py could mostly proxy to the “real” setup.py (the upstream package) then apply patches after installation. The one issue I’m not sure about is how to handle getting the upstream package. Do you distribute the whole thing? Could you recursively call out to the installer? Well, distributing the upstream version with the patches is clearly the easiest.

  2. Haha, that’s really funny that you named your version omelette too without knowing about mine. Feel free to contribute to collective.recipe.omelette 🙂

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