A point worth raising: pinning versions of dependencies in your reusable Python packages is a great way of creating conflicts. e.g.: package A requires lxml==2.2.0 and package B requires lxml==2.2.1. Both packages may even work with lxml 2.2.2, but by being overly specific you've created a packaging conflict.

Perhaps a caveat should apply to this article -- it's only applicable to deployments, not to Python packages intended for third-party use.