glep added the comment:
Actually I have come to realise that this is the intended behaviour for source
distributions. And that it is simply not possible to pull in a package from
outside the current top-level package when building a source distribution.
--
resolution: -> not a
New submission from glep:
Suppose I have a setup.py with the option
...
packages=['package', 'package.utils'],
package_dir={'package.utils', '../utils'},
...
as would arise if ../utils was a package shared between several projets
('pa