[Python-ideas] improve compatibility

[Andrew Barnert]

On Nov 28, 2014, at 8:29, Liam Marsh <liam.marsh.home at gmail.com> wrote:

> hello,
> the problem is that even with extreme precaution, it is impossible to keep ALL modules compatible from a version to another.

Do you have a specific library or app that you've had a problem with? There were a handful of modules that had a problem with the 3.2 to 3.3 conversion, but every one I saw was caused by language and implementation changes, not stdlib changes. I don't think I've seen anything that works with 3.3 but not 3.4. I'm sure it's not impossible for such a thing to happen, but it would be helpful to have at least one real-life example.

> 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__.

But how would this work? The same changes that broke a handful of third-party modules between 3.2 and 3.3 probably also mean that the 3.2 stdlib wouldn't work in 3.3 without minor changes. And as for builtins, most of those are exposing internals of the implementation, so trying to make the 3.2 builtins work with 3.3 would take a lot more work than just building the 3.2 code against 3.3.

> -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.
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