Python only shows the deprecation warnings on initial run [1].
[1] https://bugs.python.org/issue30091
To work around this add the "-B" option to python invocation.
7.3 is the oldest image available on TravisCI that works. Older 6.4
version does not play well with Enchant, resulting in a build error.
This could probably be averted by trying to build with 6.4 and without
Enchant support, but I'm not sure if it's worth it.