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 ?

The question I would ask is why do you want to do this. If your import machine is not working correctly, is there a way that you can fix it, rather than resorting to modifying the PYTHONPATH, something which is essentially a hack. — user2138149
– user2138149, Commented Jun 30, 2024 at 19:27

Community · Accepted Answer · 2017-05-23 12:18:20Z

317

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, 2017 at 12:18

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answered Apr 19, 2013 at 22:49

Ned Deily

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8 Comments

UnadulteratedImagination Over a year ago

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

R Claven Over a year ago

Hey man, this broke my django. Are you sure you mean to tell people to put it at the top?!?!!?

Ned Deily Over a year ago

@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?

HiFile.app - best file manager Over a year ago

just a side note: sys.path is zero-indexed as any list, so it should be sys.path.insert(0, '/path/to/mod_directory')

kadee Over a year ago

You really should use "1" instead of "0"! Otherwise you break sys.path. See also stackoverflow.com/q/10095037/125507.

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Thomas Weller · Accepted Answer · 2025-08-04 11:51:43Z

21

You could use:

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

edited Aug 4 at 11:51

Thomas Weller

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answered Aug 5, 2017 at 12:47

Δημητρης Παππάς

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2 Comments

sanjivgupta Over a year ago

you need ';' in windows.

luckydonald Over a year ago

Just use os.pathsep instead of ':' or ';'.

Caridorc · Accepted Answer · 2024-07-10 12:15:14Z

13

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.

edited Jul 10, 2024 at 12:15

Caridorc

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answered Jul 16, 2018 at 8:47

Jayhello

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2 Comments

Gang Over a year ago

The simplest is the best answer, add this for development will make the autocomplete work

Athar Over a year ago

I have updated the .bashrc as explained above but did not reflect in the jupyter notebook. Jupyter notebook still says module not found.

AlexMakarov · Accepted Answer · 2024-03-06 09:59:38Z

3

import sys
import os

sys.path.append(os.path.dirname(os.path.abspath(__file__)))

is a general approach to add folder where the script is placed into syspath. Helps with Python 3 if you are running script from different places but still want imports to work.

answered Mar 6, 2024 at 9:59

AlexMakarov

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Comments

Alexander Pacha · Accepted Answer · 2018-02-23 16:19:53Z

2

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

answered Feb 23, 2018 at 16:19

Alexander Pacha

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Comments

user3517603 · Accepted Answer · 2018-02-16 16:19:01Z

1

Temporarily changing dirs works well for importing:

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

answered Feb 16, 2018 at 16:19

user3517603

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2 Comments

ssc Over a year ago

This doesn't seem to work; fails here on Python 3.8.11 with No module named '<module>'.

Hardik Kamboj Over a year ago

You need to replace <module> with the module name you are trying to import

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