Adding folder to Python's path permanently

Question

I've written a library in python and I want it to reside in a common location on the file system.

From my script, I just want to do:

>>> import mylib

Now I understand that in order to do this, I can do this:

>>> import sys
>>> sys.path.append(r'C:\MyFolder\MySubFolder')
>>> import mylib

But I don't want to have to do that every time.

The question is: How do I add a folder to python's sys.path permanently? I would imagine that it would be an environment variable, but I can't find it.

It seems like it should be easy, but I can't find out how to do it.

Answer 1

The PYTHONPATH environment variable will do it.

Answer 2

Deducing from the path you provided in your example here's a tutorial for setting the PYTHONPATH variable in Windows: http://docs.python.org/using/windows.html#excursus-setting-environment-variables

Answer 3

Another possibility is to alter the sys.path in your sitecustomize.py, a script that is loaded as Python startup time. (It can be put anywhere on your existing path, and can do any setup tasks you like; I use it to set up tab completion with readline too.)

The site module offers a method that takes care of adding to sys.path without duplicates and with .pth files:

import site
site.addsitedir(r'C:\MyFolder\MySubFolder')