Standalone applications ?

[TPJ]

It's just the same as with Java, GTK+, Qt or any other
library/platform. If you're doing development with Java, you can use
any version that you like (for example the version 1.5) - and your
application probably won't be able to run by an older version of Java.
The same is with, for example, GTK+ library - if you use the version
2.6, your application might not work on systems with older version of
the GTK+ library.

And the same is with Python. When you develop application with Python,
you must use some version of Python - and this is your dependency. You
might say that your application needs a particular version of Python
(and eventually particular versions of external modules).