[Tutor] accessing modules found throughout a package?

[Alex Kleider]

On 2015-10-17 19:49, Steven D'Aprano wrote:

> which will work from your package's callers, and from within the 
> package
> itself provided the top level directory can be found within Python's
> path. Within the package you can also use relative imports, see the
> docs for more detail.

How does one arrange so "the top level directory _can_ be found within 
Python's path."?