* Scott Kitterman <debian@kitterman.com>, 2012-03-17, 14:29:
Upon reflection, this could be better stated something like this:"The generated minumum dependency may be different than the lowest version currently supported. In such cases, X-Python-Version must still be specified if the generated dependency is not sufficient."To give a specific example, even though python3.2 is the only supported python3, for an arch all module, dh_python3 will generate a dependency of python3 >= 3.1.3-13. If the upstream code requires 3.2, then you still need to specify (in this example) X-Python3-Version.
This is true, but I'm not sure why Python Policy needs to talk about this. If it does, then probably appendix B would be the correct place. Or a footnote.
In general, how X(S)P(3)V is translated to dependency on python(3) varies depending on which helper you use. A packaging helper can add a dependency on "python(3) (>= $V)" for several reasons:
1) because the package declared "X(S)P(3)V: >= $V" [all helpers];2) because the package ships extension modules (or other files that cannot be shared across versions) only for versions >= $V [all helpers];
3) because the helper is implemented in such a way that it supports at runtime only (a subset of) versions available at buildtime [dh_python2, and sometimes python-central];
4) because it generates maintainer scripts that need such version of python(3) [dh_python2, dh_python3].
-- Jakub Wilk