Importing modules from parent folder

Question

I am running Python 2.5.

This is my folder tree:

ptdraft/
  nib.py
  simulations/
    life/
      life.py

(I also have __init

Answer 1

Here is an answer that's simple so you can see how it works, small and cross-platform.
It only uses built-in modules (os, sys and inspect) so should work
on any operating system (OS) because Python is designed for that.

Shorter code for answer - fewer lines and variables

from inspect import getsourcefile
import os.path as path, sys
current_dir = path.dirname(path.abspath(getsourcefile(lambda:0)))
sys.path.insert(0, current_dir[:current_dir.rfind(path.sep)])
import my_module  # Replace "my_module" here with the module name.
sys.path.pop(0)

For less lines than this, replace the second line with import os.path as path, sys, inspect,
add inspect. at the start of getsourcefile (line 3) and remove the first line.
- however this imports all of the module so could need more time, memory and resources.

The code for my answer (longer version)

from inspect import getsourcefile
import os.path
import sys

current_path = os.path.abspath(getsourcefile(lambda:0))
current_dir = os.path.dirname(current_path)
parent_dir = current_dir[:current_dir.rfind(os.path.sep)]

sys.path.insert(0, parent_dir)

import my_module  # Replace "my_module" here with the module name.

It uses an example from a Stack Overflow answer How do I get the path of the current executed file in Python? to find the source (filename) of running code with a built-in tool.

from inspect import getsourcefile  
from os.path import abspath  

Next, wherever you want to find the source file from you just use:

abspath(getsourcefile(lambda:0))

My code adds a file path to sys.path, the python path list
because this allows Python to import modules from that folder.

After importing a module in the code, it's a good idea to run sys.path.pop(0) on a new line
when that added folder has a module with the same name as another module that is imported
later in the program. You need to remove the list item added before the import, not other paths.
If your program doesn't import other modules, it's safe to not delete the file path because
after a program ends (or restarting the Python shell), any edits made to sys.path disappear.

Notes about a filename variable

My answer doesn't use the __file__ variable to get the file path/filename of running
code because users here have often described it as unreliable. You shouldn't use it
for importing modules from parent folder in programs used by other people.

Some examples where it doesn't work (quote from this Stack Overflow question):

• it can't be found on some platforms • it sometimes isn't the full file path

• py2exe doesn't have a __file__ attribute, but there is a workaround
• When you run from IDLE with execute() there is no __file__ attribute
• OS X 10.6 where I get NameError: global name '__file__' is not defined