On Fri, Mar 29, 2013 at 3:55 PM, Nick Coghlan <ncoghlan@gmail.com> wrote:
No, mutating sys.path for versioned imports is a broken design. You end up with two possibilities:
* If you append, then you can't override modules that have a default version available on sys.path. This is not an acceptable restriction, which is why pkg_resources doesn't do it that way * If you prepend, then you have the existing pkg_resources failure mode where it can accidentally shadow more modules than intended. This is a nightmare to debug when it goes wrong (it took me months to realise this was why a system install of the main application I work on was shadowing the version in source checkout when running the test suite or building the documentation).
The correct way to do it is with a path hook that processes a special "<versioned-packages>" marker label in sys.path (probably placed after the standard library but before site-packages by default). Any mounted directories would be tracked by that path hook, but never included directly in sys.path itself.
How is that different from replacing "<versioned-packages>" with the path of the versioned package being added?