Python version dependencies in pkg

All,

A quick question:

If a pkg depends on python, but not a specific version, it will simply pick a version to install (I guess, whatever version was the default when the pkg was built, 3.8 right now), correct?

If you have 3.9 installed, that will satifsfy dependencies, and it won't install python3.8, correct? Or are the dependent versions for interpretec languages in pkg locked to whatever the default is?

Assuming "any python will work", If you have 3.8 installed, and later install 3.9 -- is there any easy way to point your package at the new version as the new dependency, without deinstalling/reinstalling it?

-Dan