python - Using .pth files

Question

I am trying to make a module discoverable on a system where I don't have write access to the global site-packages directory, and without changing the environment (PYTHONPATH). I have tried to place a .pth file in the same directory as a script I'm executing, but it seems to be ignored. E.g., I created a file extras.pth with the following content:

N:PythonExtraslibsite-packages

But the following script, placed and run in the same directory, prints False.

import sys
print r"N:PythonExtraslibsite-packages" in sys.paths

The only directory in sys.path to which I have write access is the directory containing the script. Is there another (currently non-existent) directory where I could place extras.pth and have it be seen? Is there a better way to go about this?

I'm using python 2.7 on Windows. All .pth questions I could find here use the system module directories.

Edit: I've tracked down the Windows per-user installation directory, at %APPDATA%PythonPython27site-packages. I can place a module there and it will be imported, but if I put a .pth file there, it has no effect. Is this really not supposed to work, or am I doing something wrong?

Answer 1

As described in the documentation, PTH files are only processed if they are in the site-packages directory. (More precisely, they are processed if they are in a "site directory", but "site directory" itself is a setting global to the Python installation and does not depend on the current directory or the directory where the script resides.)

If the directory containing your script is on sys.path, you could create a sitecustomize.py in that directory. This will be loaded when Python starts up. Inside sitecustomize.py, you can do:

import site
site.addsitedir('/some/dir/you/want/on/the/path')

This will not only add that directory, but will add it as a "site directory", causing PTH files there to be processed. This is handy if you want to create your own personal site-packages-like-directory.

If you only need to add one or two directories to the path, you could do so more simply. Just create a tiny Python library that manipulates sys.path, and then import that library from your script. Something like:

# makepath.py
import sys
sys.path.append('/whatever/dir/you/want')

# script.py
import makepath

Edit: Again, according to the documentation, there is the possibility of a site-specific directory in %APPDATA%PythonPythonXYsite-packages (on Windows). You could try that, if in fact you have write access to that (and not just to your script directory).