While working with the Yum driver for Bcfg2 (a configuration management tool) I came across an interesting problem.  Bcfg2 would load the driver and Yum would read all its configuration and .repo files.  Next, Bcfg2 would attempt to install files and packages according to its specification.  Bcfg2 would gladly install additional .repo files for Yum, but the Yum driver would have no knowledge of them and wouldn’t be able to install packages from the new repo.  You would have to run the Bcfg2 client again for the Yum driver to proper install the new packages.  A bug, and it was time to fix it.

Turns out, using the Yum API, there isn’t a way to reset or reload the .repo files without a lot of work.  All my attempts just removed all repos from Yum’s little mind rendering it unable to install any package.  A suggestion from the Yum-devel mailing list was to simply reinstantiate the Yum API. So,

import yum
b = yum.YumBase()
...do interesting things...
b = yum.YumBase()
...do interesting things with updated .repo files...

As I was cleanly between transactions at that point in the code, this worked very well.

My Bcfg2 patches and work can be found at GitHub: https://github.com/jjneely/bcfg2