[Tutor] What is the best way for a program suite to know where it is installed?

[boB Stepp]

I was just re-reading the entire thread at
    https://www.mail-archive.com/tutor@python.org/msg77864.html
And I have asked similar questions previous to that thread.  I still
do not have a satisfactory answer for the subject line's question that
both makes sense to me and seems to be good programming practice.  And
that works for any OS that the program suite is installed under.

A constantly recurring situation I am having is a programming project
with a nested directory structure.  Usually I will have "tests" and
"data" folders nested under the top level project folder.  There may
be others as well depending on the complexity of the project I am
attempting.  As far as I can tell, I cannot make any assumptions about
what the current working directory is when a user starts the program.
So how can one of my programs *know* what the absolute path is to,
say, the top level of the program suite?  If I could always reliably
determine this by my program's code, every other location could be
determined from the known nested structure of the program suite.  [But
I have a dim recollection that either Ben or Cameron thought relying
on the "known nested structure" is brittle at best.]

So far the best method I've come up with is to make use of "__file__"
for the initiating program file.  But from past discussions I am not
certain this is the *best* way.  Is the *best* way going to get me
into best techniques for installing and distributing programs?  If so,
this strikes me as a huge mess to dive into!

TIA!
-- 
boB