adding directory to sys.path /PYTHONPATH

Question

I am trying to import a module from a particular directory.

The problem is that if I use sys.path.append(mod_directory) to append the path and then open the python interpreter, the directory mod_directory gets added to the end of the list sys.path. If I export the PYTHONPATH variable before opening the python interpreter, the directory gets added to the start of the list. In the latter case I can import the module but in the former, I cannot.

Can somebody explain why this is happening and give me a solution to add the mod_directory to the start, inside a python script ?

I have tried [`site` module](https://docs.python.org/3/library/site.html#site.addsitedir). — Zeinab Abbasimazar, Sep 17 '17 at 07:27

score 269 · Accepted Answer · edited May 23 '17 at 12:18

269

This is working as documented. Any paths specified in PYTHONPATH are documented as normally coming after the working directory but before the standard interpreter-supplied paths. sys.path.append() appends to the existing path. See here and here. If you want a particular directory to come first, simply insert it at the head of sys.path:

import sys
sys.path.insert(0,'/path/to/mod_directory')

That said, there are usually better ways to manage imports than either using PYTHONPATH or manipulating sys.path directly. See, for example, the answers to this question.

edited May 23 '17 at 12:18

Community

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answered Apr 19 '13 at 22:49

Ned Deily

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thanks for the reply. The problem was that I didn't realize that to add module packaged as a .egg file you have to include the filename instead of just the directory in python 2.6 – UnadulteratedImagination Apr 20 '13 at 23:41
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Hey man, this broke my django. Are you sure you mean to tell people to put it at the top?!?!!? – R Claven Oct 12 '14 at 05:50
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@RClaven, sorry, it's hard to tell what action and results you are referring to: "put it at the top" and "broke my django" aren't very precise. Can you elaborate? – Ned Deily Oct 12 '14 at 06:40
For more about how sys.path works, see this answer http://stackoverflow.com/a/38403654/850326 – djhaskin987 Jul 15 '16 at 20:17
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just a side note: `sys.path` is zero-indexed as any list, so it should be `sys.path.insert(0, '/path/to/mod_directory')` – HiFile.app - best file manager Mar 06 '17 at 09:00
@V.K.Thanks for noticing that after all this time! Fixed. – Ned Deily Mar 07 '17 at 15:00
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You really should use "1" instead of "0"! Otherwise you break [sys.path](https://docs.python.org/3/library/sys.html#sys.path). See also http://stackoverflow.com/q/10095037/125507. – kadee Feb 14 '18 at 09:01

score 18 · Answer 2 · answered Aug 05 '17 at 12:47

18

You could use:

import os
path = 'the path you want'
os.environ['PATH'] += ':'+path

answered Aug 05 '17 at 12:47

Δημητρης Παππάς

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you need ';' in windows. – sanjivgupta Jul 05 '20 at 02:49

score 12 · Answer 3 · answered Jul 16 '18 at 08:47

12

As to me, i need to caffe to my python path. I can add it's path to the file /home/xy/.bashrc by add

export PYTHONPATH=/home/xy/caffe-master/python:$PYTHONPATH.

to my /home/xy/.bashrc file.

But when I use pycharm, the path is still not in.

So I can add path to PYTHONPATH variable, by run -> edit Configuration.

answered Jul 16 '18 at 08:47

Jayhello

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The simplest is the best answer, add this for development will make the autocomplete work – Gang Aug 10 '18 at 22:25
I have updated the .bashrc as explained above but did not reflect in the jupyter notebook. Jupyter notebook still says module not found. – Athar Jan 09 '19 at 14:03

score 2 · Answer 4 · answered Feb 23 '18 at 16:19

When running a Python script from Powershell under Windows, this should work:

$pathToSourceRoot = "C:/Users/Steve/YourCode"
$env:PYTHONPATH = "$($pathToSourceRoot);$($pathToSourceRoot)/subdirs_if_required"

# Now run the actual script
python your_script.py

score 1 · Answer 5 · answered Feb 16 '18 at 16:19

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Temporarily changing dirs works well for importing:

cwd = os.getcwd()
os.chdir(<module_path>)
import <module>
os.chdir(cwd)

answered Feb 16 '18 at 16:19

user3517603

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This doesn't seem to work; fails here on Python 3.8.11 with `No module named ''`. – ssc Aug 30 '21 at 04:34

adding directory to sys.path /PYTHONPATH

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