How to organize Python files in a (relatively) big project

[The Eternal Squire]

I, too have often come up against the inconvenience of creating
libraries that I want to reuse but that do not want to incorporate into
the Python library.   I came up with this Python library addition to
automagically add the directory of where a module resides that I want
to import to the system path, so that I can simply add the module by
name without needing to worry about anything else.

The large advantage of this is that I can now import from adjacent
directories rather than subordinate ones.    For best results in large
projects with deep tree structure, the paths of the importing script
and the imported module should have at least 3 levels in common.  I do
not consider typing 3 levels of pathing as a hint to be a great
inconvenience.

It ain't perfect, it ain't Zen, but for me this has worked from Python
2.2 and up with very few problems for projects up to 1000 files.
Improvements, anyone?

The Eternal Squire

#----------------------relative.py---------------------
# Place in Python##\Lib
#
import sys
from   inspect import getfile
from   os.path import abspath


backslash = '\\'



def caller ():

    'name of the calling script'

    frame     = sys._getframe(1)
    if not frame:  return ''
    frame = frame.f_back
    if not frame:  return ''
    result = getfile (frame)
    if result[-4:].lower () in ['.pyc', '.pyo']: result = filename[:-4]
+ '.py'
    return abspath (result)



def append (path):

    'append relative path to system module search path'


    if not path:     return

    try:
        calling_script = caller ()

        top_path       = path.split          (backslash)[0]
        where          = calling_script.find (top_path + backslash)

        if where < 0:  return
        result         = calling_script [:where] + path

        if result not in sys.path:  sys.path.append (result)
        return result


    except:
        return ''
#---------------------end of relative.py---------------#

#---------------------"A\B\C\more levels\importer.py"-----------------#
#prototypical code, do not try to execute

import relative
relative.append ("\A\B\C\subpath")  # no file extension!
from module import whatsit               # module resides under subpath
whatsit ()