[Python-ideas] improve compatibility

hello, the problem is that even with extreme precaution, it is impossible to keep ALL modules compatible from a version to another. what I want to ask is this: -some "packs" which can, like py-compile, generate .pyc files, but using "old" versions of the default library, and of __builtins__. -One will go with every minor version and will be optionnal in the installation -any imported py file will be able to choose which version it wants with the "#! py recommended version X.X" or "#! py mandatory version X.X" commentaries at the begining of the file. thank you and have a nice day/evening/night.