Develop Reference

Remove path from $PATH macOS Mojave

I am trying to set up my new MacBook, and installed python 3.7, however realised that I would rather use python 3.6. I uninstalled python 3.7, however the python path is still in my $PATH alongside the path for python 3.6. The questions which I have seen on this topic seem to give answers which involve using export PATH which only changes the path for the current session, or say that the measure which needs to be taken depends on your system configuration and version of macOS
echo $PATH gives:
/Library/Frameworks/Python.framework/Versions/3.6/bin:/opt/local/bin:/opt/local/sbin:/Library/Frameworks/Python.framework/Versions/3.7/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:
I have already deleted the ../3.7 which is being pointed to, so would like to only have the 3.6 path in $PATH

You may use export PATH=/Library/Frameworks/Python.framework/Versions/3.6/bin:/opt/local/bin:/opt/local/sbin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:, but write it in the .bash_profile or the .bashrc in your user.
That is, if you are using bash.
Maybe you will find already a definition of PATH in there, so you can just change it.

Go to your home directory, cd ~.
Open .bash_profile file.
Like so,
open .bash_profile
Make changes to the path variable in the end of the file.
Save and exit.
Now close the current terminal and open new one. The changes will sustain.
Also for using python of your wish you can alias it in .bash_profile (obviously after setting PATH variable).
Like,
alias python="python3.6"

Impossible to set python.exe to *.py scripts on Win7

i've installed py 2.7 (64bit) on my PC with Win7 (64bit) without problem but I'm not able to run *.py scripts via DOS shell without declare python full path.
Let me better explain :
If I type D:\ myscript.py it doesn't work. The script is open with wordpad
If I type D:\ C:\Python27 myscript.py it works and run correctly
I try to change the default application software for *.py file via Win7 GUI ( control pannel etc etc) but without success.
Python is not present in the list of available sw and in any case also with the manual set I'm not able to associate python.exe at *.py files.
I've checked in my environment variables but I've not found problem (python path is declared in Path = C:\Python27\;C:\Python27\Scripts).
I've tried also to modify HKEY_CLASSES_ROOT->Applications->python.exe->shell->open->command :
old register value "C:\Python27\python.exe" "%1"
new register value "C:\Python27\python.exe" "%1" %*
without success.
Any suggestion?
Thanks

Here is another check to make, which helped me figure out what was going on.
I switched from the 32bit Anaconda to the 64bit version. I deinstalled, downloaded then reinstalled, but several things didn't get cleaned up properly (quick launch stuff, and some registry keys). The problem on my side was that the default installation path changed, from C:\Anaconda to C:\Anaconda2.
I first tried the assoc and ftype tricks, everything was fine there. However, the HKEY_CLASSES_ROOT\Applications\python.exe\shell\open\command registry key was pointing to the old Anaconda path. As soon as I fixed this, python.exe showed up when I tried associating with "Open with" and everything went back to normal.
I also added the %* at the end in the registry key.

You could try to use the ASSOCIATE command in CMD:
ASSOCIATE .py C:\PathTo\python.exe
More information at http://ss64.com/nt/associate.html

#slv 's answer is good and helped me a bit with solving this problem. Anyhow, since I had previous installations of Python before this error occured for me, I might have to add something to this. One of the main problems hereby was that the directory of my python-installation changed.
So, I opened regedit.exe and followed these to steps:
I searched the entire registry for .py, .pyw, .pyx and .pyc (hopefully I did not forget to mention any here). Then, I radically deleted all occurrences I could find.
I searched the entire registry for my old python-installation-path (e.g. C:\Users\Desktop\Anaconda3). Then I replaced this path with my new installation path (e.g. C:\Users\Desktop\Miniconda3). Thereby, I also came across and replaced HKEY_CLASSES_ROOT\Applications\python.exe\shell\open\command which #slv mentioned.
Afterwards, it was possible again to connect a .py-file from the Open with...-menu with my python.exe.

The *.py file is a source code file. If you set up your system environment correctly, you need to run python myscript.py
the following answer is related to your question
Making Python scripts run on Windows without specifying ".py" extension

Do you know that when you change the default application of a file, you are able to browse for the application?
You can click on the "browse" button (as shown in the red rectangle), then choose C:\Python27\python.exe.
Also remember to click on the "Always use this program to open this program" checkbox, which is shown in the green rectangle, so that win7 knows how to open this file the next time you ask it to open *.py file.
Then I believe you'll be able to run myScript.py simply by typing "myScript.py" in the correct dirctory in DOS shell.
After doing all the above steps, be sure to reopen a new command shell.

How to import modules from alternate locations when using Python IDLE?

I've been trying to figure this out for more than 2 days, screening the internet and the tutorial, but yet I don't have solved my problem. I'm a real newb and don't yet really know what I'm doing..
Software I use:
Mac OS X 10.6
Python v3.2.2
Interactive interpreter (IDLE)
Problem:
IDLE's default directory is /Users/ME/Documents/. Files with the extention .py can only be opened when located in this directory. However, I made a folder where I would like to save all the .py files etc that have to do with this software. Currently, IDLE cannot load .py files from the chosen directory by me.
What I did first was I added to IDLE:
import sys.
sys.path.append('Users/Mydir/')
sys.path
However, in an already existing thread from 2010 I read sys.path is for the Interpreter ONLY, and that if I am to change this I need to modify the PYTHONPATH environment variable:
PYTHONPATH="/Me/Documents/mydir:$PYTHONPATH"
export PYTHONPATH
However, I'm confused how to use this and cannot find answers to my following questions:
1) PYTHONPATH (.py?) is already existing on my computer when I installed the program?
If YES, where is it? I cannot find it anywhere.
If NO, I need to create one. But where and what should be the content so that IDLE can load files from a non-default directory? Should it contain only the words in bold?
I hope I made my problem clear.
Cheers

It's not totally clear to me what you mean by load. That could mean Open and Close files in the IDLE editor. Or it could mean being able to use the Python import statement to load existing Python modules from other files. I'll assume the latter, that by load you mean import.
There are two general ways to launch IDLE on Mac OS X. One is from the command line of a terminal session; if you installed Python 3.2 using the python.org installers, by default typing /usr/local/bin/idle3.2 will work. The other way is by launching IDLE.app from /Applications/Python 3.2, i.e. by double-clicking its icon. Because you say the default directory for files is your Documents folder, I'm assuming you are using the second method because IDLE.app sets Documents as its current working directory, which becomes the default directory for *Open*s and *Save*s and is automatically added as the first directory on Python's sys.path, the list of directories that Python uses to search for modules when importing.
If you want to add other directories to sys.path, as you've noted you can use the PYTHONPATH environment variable to do so. The standard way to do this is to add an export PYTHONPATH=... definition to a shell startup script, like .bash_profile. However, if you use IDLE.app, no shell is involved so commands in .bash_profile have no effect.
While there are ways to modify the environment variables for OS X GUI apps, in this case, a simpler solution is to use the other method to invoke IDLE, from the command line of a shell session, using either /usr/local/bin/idle3.2 or, if you've run the Update Shell Profile command in the /Applications/Python 3.2 folder (and opened a new terminal session), just idle3. Then, a PYTHONPATH environment variable you set up will be inherited by that IDLE.
BTW, there is no direct way to modify the initial current working directory of IDLE.app from Documents other than modifying the code in IDLE. If you start IDLE from a command
line, it inherits the current working directory of the shell.
[UPDATE] But rather than fooling around with defining PYTHONPATH, here is another even simpler, and probably better, approach that should work with either IDLE.app or the command line idle. It takes advantage of Python path configuration (.pth) files and user site-package directories. Assuming you are using a standard Python framework build of 3.2 (like from a python.org installer) on Mac OS X, create a path file for the directory you want to permanently add to sys.path. In a terminal session:
mkdir -p ~/Library/Python/3.2/lib/python/site-packages
cd ~/Library/Python/3.2/lib/python/site-packages
cat >my_paths.pth <<EOF
/Users/YOUR_USER_NAME/path/to/your_additional_python_directory_1
/Users/YOUR_USER_NAME/path/to/your_additional_python_directory_2
EOF
Now, whenever you run that Python 3.2 or IDLE under your user name, the directories you have added to the .pth file will automatically be added to sys.path.
BTW, the exact path location of the user site-packages directory for versions of Python earlier than 3.2 or 2.7 may be slightly different. Also, on other Unix-y systems, the default location for the user site-package directory is ~/.local/lib/python3.2/site-packages.

PYTHONPATH is an environment variable (see here and here). I don't have a Mac, but from the threads I have linked to you would type something like
launchctl setenv PYTHONPATH=/Me/Documents/mydir:$PYTHONPATH
on the command line to allow you to run Python scripts from /Me/Documents/mydir. Alternatively, put this line in a file called .bashrc in your home directory (~) and this path will be set each time each time you open a terminal. See here for a short introduction to .bashrc and other .bash* files. Hope that helps.
EDIT See also this question.

Mac Swampy (Python learning module) install

I thought I would teach my kids programming and am using "Think Python" by Downey. The book is great except when he gets to installing "Swampy" a Turtle-like learning module. I've spent a few hours trying to figure it out--now I need help.
Can anyone offer a clear, step-by-step set of instructions on how to install Swampy? Please assume zero prior knowledge of Unix, etc.
I'm on OS X (10.6.6). Python is running fine. Tkinter is fine.
Here are the overall installation instructions offered at the author's site:
http://www.greenteapress.com/thinkpython/swampy/install.html
I am stuck at the "Add Swampy to your search path" section.
Here are the additional instructions the author points to regarding the search path:
http://docs.python.org/install/index.html#inst-search-path
Probably terribly obvious buy tough stuff for an intro text!
Update
A few details for the record for anyone who comes across this later:
My installation does not have a file or folder "python2" so the pathname "/home/downey/swampy-2.0/python2" might not work. I just dropped the "python2" and all was well.
Had a bit of a problem finding the bashpc or bash_profile file. Didn't seem to exist even when looking for hidden files. So I just created a new one. All seems well.
Thanks again for your help--I would never have figured it out :)
I'm surprised there isn't some sort of installer or script to handle this given the audience for the book (newbies like me). :)

Open the terminal and navigate to the folder where you unzipped Swampy. Find the full directory path of that location by typing pwd. Let's say that location is /home/downey/swampy-2.0/python2. Now in the terminal issue this command export PYHTONPATH="/home/downey/swampy-2.0/python2". This will set the PYTHONPATH environment variable.
If that works fine, you need to make sure that this always runs when you open the terminal. For that you need to edit a file called .bashrc on your computer.
In the terminal, try nano ~/.bashrc.
That will open a simple text editor. In that file add the same line export PYHTONPATH="/home/downey/swampy-2.0/python2". Type Ctrl+X to close and make sure you save.
Now instead of always setting the environment variable manually, you can just do source ~/.bashrc and that will execute the command for you.
Note that every time you exit and reopen the terminal, you need to run source ~/.bashrc for the PYTHONPATH to be set.If you don’t want to run source ~/.bashrc every time you open the terminal, you can configure the Terminal to automatically run this command at startup (i.e. when the terminal window is opened). To do that –
Go to Terminal –> Preferences –> Settings –> Shell.
Check ‘Run Command’ and enter source ~/.bashrc.
NOTE: These settings are only need to be applied to each profile separately. For example if you applied these settings to the Basic profile, they won’t be applicable to Grass profile.
Hope this helps!

An easy way to add variables to your path is to add them to your .bash_profile, which is located in your home directory. This file loads every time you open up terminal. It is a hidden file, so you will not be able to view it (by default) in Finder. Run this command after opening a new terminal window:
open -a TextEdit .bash_profile
This will open the profile up in a new TextEdit window. Add this & save:
PYTHONPATH=${PYTHONPATH}:/home/downey/swampy-2.0/python2
export PYTHONPATH
Assuming your Swampy download path is the same from the Web Site (/home/downey/swampy-2.0/python2), the next time you run terminal, the path should now be included.

Permanently add a directory to PYTHONPATH?

Whenever I use sys.path.append, the new directory will be added. However, once I close python, the list will revert to the previous (default?) values. How do I permanently add a directory to PYTHONPATH?

If you're using bash (on a Mac or GNU/Linux distro), add this to your ~/.bashrc
export PYTHONPATH="${PYTHONPATH}:/my/other/path"

You need to add your new directory to the environment variable PYTHONPATH, separated by a colon from previous contents thereof. In any form of Unix, you can do that in a startup script appropriate to whatever shell you're using (.profile or whatever, depending on your favorite shell) with a command which, again, depends on the shell in question; in Windows, you can do it through the system GUI for the purpose.
superuser.com may be a better place to ask further, i.e. for more details if you need specifics about how to enrich an environment variable in your chosen platform and shell, since it's not really a programming question per se.

Instead of manipulating PYTHONPATH you can also create a path configuration file. First find out in which directory Python searches for this information:
python -m site --user-site
For some reason this doesn't seem to work in Python 2.7. There you can use:
python -c 'import site; site._script()' --user-site
Then create a .pth file in that directory containing the path you want to add (create the directory if it doesn't exist).
For example:
# find directory
SITEDIR=$(python -m site --user-site)
# create if it doesn't exist
mkdir -p "$SITEDIR"
# create new .pth file with our path
echo "$HOME/foo/bar" > "$SITEDIR/somelib.pth"

This works on Windows
On Windows, with Python 2.7 go to the Python setup folder.
Open Lib/site-packages.
Add an example.pth empty file to this folder.
Add the required path to the file, one per each line.
Then you'll be able to see all modules within those paths from your scripts.

In case anyone is still confused - if you are on a Mac, do the following:
Open up Terminal
Type open .bash_profile
In the text file that pops up, add this line at the end:
export PYTHONPATH=$PYTHONPATH:foo/bar
Save the file, restart the Terminal, and you're done

You could add the path via your pythonrc file, which defaults to ~/.pythonrc on linux. ie.
import sys
sys.path.append('/path/to/dir')
You could also set the PYTHONPATH environment variable, in a global rc file, such ~/.profile on mac or linux, or via Control Panel -> System -> Advanced tab -> Environment Variables on windows.

To give a bit more explanation, Python will automatically construct its search paths (as mentioned above and here) using the site.py script (typically located in sys.prefix + lib/python<version>/site-packages as well as lib/site-python). One can obtain the value of sys.prefix:
python -c 'import sys; print(sys.prefix)'
The site.py script then adds a number of directories, dependent upon the platform, such as /usr/{lib,share}/python<version>/dist-packages, /usr/local/lib/python<version>/dist-packages to the search path and also searches these paths for <package>.pth config files which contain specific additional search paths. For example easy-install maintains its collection of installed packages which are added to a system specific file e.g on Ubuntu it's /usr/local/lib/python2.7/dist-packages/easy-install.pth. On a typical system there are a bunch of these .pth files around which can explain some unexpected paths in sys.path:
python -c 'import sys; print(sys.path)'
So one can create a .pth file and put in any of these directories (including the sitedir as mentioned above). This seems to be the way most packages get added to the sys.path as opposed to using the PYTHONPATH.
Note: On OSX there's a special additional search path added by site.py for 'framework builds' (but seems to work for normal command line use of python): /Library/Python/<version>/site-packages (e.g. for Python2.7: /Library/Python/2.7/site-packages/) which is where 3rd party packages are supposed to be installed (see the README in that dir). So one can add a path configuration file in there containing additional search paths e.g. create a file called /Library/Python/2.7/site-packages/pip-usr-local.pth which contains /usr/local/lib/python2.7/site-packages/ and then the system python will add that search path.

On MacOS, Instead of giving path to a specific library. Giving full path to the root project folder in
~/.bash_profile
made my day, for example:
export PYTHONPATH="${PYTHONPATH}:/Users/<myuser>/project_root_folder_path"
after this do:
source ~/.bash_profile

On linux you can create a symbolic link from your package to a directory of the PYTHONPATH without having to deal with the environment variables. Something like:
ln -s /your/path /usr/lib/pymodules/python2.7/

For me it worked when I changed the .bash_profile file. Just changing .bashrc file worked only till I restarted the shell.
For python 2.7 it should look like:
export PYTHONPATH="$PYTHONPATH:/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python"
at the end of the .bash_profile file.

Adding export PYTHONPATH="${PYTHONPATH}:/my/other/path" to the ~/.bashrc might not work if PYTHONPATH does not currently exist (because of the :).
export PYTHONPATH="/my/other/path1"
export PYTHONPATH="${PYTHONPATH}:/my/other/path2"
Adding the above to my ~/.bashrc did the trick for me on Ubuntu 16.04

This is an update to this thread which has some old answers.
For those using MAC-OS Catalina or some newer (>= 10.15), it was introduced a new Terminal named zsh (a substitute to the old bash).
I had some problems with the answers above due to this change, and I somewhat did a workaround by creating the file ~/.zshrc and pasting the file directory to the $PATH and $PYTHONPATH
So, first I did:
nano ~/.zshrc
When the editor opened I pasted the following content:
export PATH="${PATH}:/Users/caio.hc.oliveira/Library/Python/3.7/bin"
export PYTHONPATH="${PYTHONPATH}:/Users/caio.hc.oliveira/Library/Python/3.7/bin"
saved it, and restarted the terminal.
IMPORTANT: The path above is set to my computer's path, you would have to adapt it to your python.

The script below works on all platforms as it's pure Python. It makes use of the pathlib Path, documented here https://docs.python.org/3/library/pathlib.html, to make it work cross-platform. You run it once, restart the kernel and that's it. Inspired by https://medium.com/#arnaud.bertrand/modifying-python-s-search-path-with-pth-files-2a41a4143574. In order to run it it requires administrator privileges since you modify some system files.
from pathlib import Path
to_add=Path(path_of_directory_to_add)
from sys import path
if str(to_add) not in path:
minLen=999999
for index,directory in enumerate(path):
if 'site-packages' in directory and len(directory)<=minLen:
minLen=len(directory)
stpi=index
pathSitePckgs=Path(path[stpi])
with open(str(pathSitePckgs/'current_machine_paths.pth'),'w') as pth_file:
pth_file.write(str(to_add))

Just to add on awesomo's answer, you can also add that line into your ~/.bash_profile or ~/.profile

The add a new path to PYTHONPATH is doing in manually by:
adding the path to your ~/.bashrc profile, in terminal by:
vim ~/.bashrc
paste the following to your profile
export PYTHONPATH="${PYTHONPATH}:/User/johndoe/pythonModule"
then, make sure to source your bashrc profile when ever you run your code in terminal:
source ~/.bashrc
Hope this helps.

I added permanently in Windows Vista, Python 3.5
System > Control Panel > Advanced system settings > Advanced (tap) Environment Variables > System variables > (if you don't see PYTHONPATH in Variable column) (click) New > Variable name: PYTHONPATH > Variable value:
Please, write the directory in the Variable value. It is details of Blue Peppers' answer.

Fix Python Path issues when you switch from bash to zsh
I ran into Python Path problems when I switched to zsh from bash.
The solution was simple, but I failed to notice.
Pip was showing me, that the scripts blah blah or package blah blah is installed in ~/.local/bin which is not in path.
After reading some solutions to this question, I opened my .zshrc to find that the solution already existed.
I had to simply uncomment a line:
Take a look

I found a solution to do this in a anaconda environment here: https://datacomy.com/python/anaconda/add_folder_to_path/
Just:
conda develop /your_path

In Python 3.6.4 you can persist sys.path across python sessions like this:
import sys
import os
print(str(sys.path))
dir_path = os.path.dirname(os.path.realpath(__file__))
print(f"current working dir: {dir_path}")
root_dir = dir_path.replace("/util", '', 1)
print(f"root dir: {root_dir}")
sys.path.insert(0, root_dir)
print(str(sys.path))
I strongly suggest you use virtualenv and virtualenvwrapper otherwise you will clutter your path

Inspired by andrei-deusteanu answer, here is my version. This allows you to create a number of additional paths in your site-packages directory.
import os
# Add paths here. Then Run this block of code once and restart kernel. Paths should now be set.
paths_of_directories_to_add = [r'C:\GIT\project1', r'C:\GIT\project2', r'C:\GIT\project3']
# Find your site-packages directory
pathSitePckgs = os.path.join(os.path.dirname(os.__file__), 'site-packages')
# Write a .pth file in your site-packages directory
pthFile = os.path.join(pathSitePckgs,'current_machine_paths.pth')
with open(pthFile,'w') as pth_file:
pth_file.write('\n'.join(paths_of_directories_to_add))
print(pthFile)

After multiple bashing into wall. Finally resolved, in my CentOS 8 the pip3 was old, which was showing error to install the recent packages.
Now, I had downloaded the Python source package, which is Python-3.10.4 and installed the usual way, however the post-installation check generated errors in bash.
And I could not remove the existing Python, because that would break the CentOS desktop features.
Solution:
For building
./configure //don't not add --prefix=/usr, which you need to set proper care
make -j8
sudo make install
Now, as you have multiple Python installed, you can set alias python=python3
And for setting PYTHONPATH
export PYTHONPATH="/usr/local/bin/python3.10:/usr/local/lib/python3.10/lib-dynload:/usr/local/lib/python3.10/site-packages"
Don't add PYTHONHOME

For those who (like me) don't want to get too deeply involved in Python file management (which seems hopelessly overcomplicated), creating a .pth file works perfectly on my Windows 11 laptop (I'm using Visual Studio Code in Windows). So just go to the folder for your virtual environment site packages - there's mine:
Create a text file with a .pth extension - I called mine wheal.pth:
Add paths to it:
The best thing about this in VS Code is that import statements recognise this path (I had to exit VS Code and go back in), so now more typing # type: ignore to suppress linting warning messages!

on Mac :
user#terminal$ env PYTHONPATH=module_path python3
>>> import sys
>>> sys.path
['module_path', 'plus_other_python3_paths',...]

Shortest path between A <-> B is a straight line;
import sys
if not 'NEW_PATH' in sys.path:
sys.path += ['NEW_PATH']