From my point of view this information is most useful for framework-like

Hi, I'd like to suggest that distutils metadata should gain a way of specifying compatibility with packages in addition to the requirement of packages. What are the use cases? - A package wants to express that it works with both Python 2 and 3. - A package wants to express that it works with TurboGears 2 or Plone 4 packages, when those do major backwards incompatible changes to their code base. In those circumstances typical question that people want to have answers to are: - For a press release of Python or a Framework, how many packages in PyPi already support the new version? - Running a particular application consisting of 200 packages, can I upgrade to the next version of Framework X? This type of information would always be optional and won't ever be used for all packages. I think it could be nonetheless helpful in many circumstances. On a side note to express this information for Python itself, it would be a good idea to expose the Python version in a distutils way, so I could also write: install_requires=['Python >= 3.0'] Comments? Hanno P.S. We want this kind of behavior for Plone, to give "plugins" to the application / framework the ability to express this information.