[Boost-build] selecting Python version for Boost.Python

Subject: [Boost-build] selecting Python version for Boost.Python
From: Stefan Seefeld (stefan_at_[hidden])
Date: 2018-02-06 18:47:21

Hello,

[Rene, I suppose you are the person most familiar with the Python
support in b2, so I suspect you know the answer to the below questions.
But this is also about consistency, so I'd like to extend the question
to understand how b2 deals with multiple values (such as for the
"toolset" feature) in general.]

I'm reviewing the b2 logic in `python.jam` as well as Boost.Python's
Jamfiles, and I'm not sure about the intended logic as far as multiple
Python versions are concerned:

With my `user-config.jam` file containing two `using python ...`
statements (with two distinct versions), is the intent for Boost.Python
being built for both ? Or only if the two differ in the major version
number (i.e., '2' and '3') ? And what about using "python=N" as
command-line option to `b2` ? if I set "N" to be a version string not
defined in my `user-config.jam` file, I get an error ("... is not a
known value of feature <python"). But if I give a "known value", nothing
happens, i.e. `b2` still builds both versions.

So what is the intended semantic for giving multiple python versions in
my `user-config.jam` file, and what is the intent for "python=N" on the
command line ?

Thanks,

        Stefan

Stefan

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