I'm going through and writing a setup doc for other developers at work for a python project and I've been reading up on the PYTHONPATH
environment variable. I'm looking at my current development system and think I have a few things set wrong that is causing my IDE (IntelliJ) to behave incorrectly when looking up the python libraries.
I've looked at the documentation here and here and I'm still unsure of what should actually be in the PYTHONPATH
environment variable.
I have PYTHONHOME
pointed to `C:\\Python27'.
My current PYTHONPATH
is set to PYTHONHOME
. Should I also add the directories from sys.path
?
UPDATE:
Based on the below information, PYTHONPATH
does not need to be set unless there are non-standard libraries that you want python to be able to find by default. For instance, when I install wxPython from the installer it will add its libraries to PYTHONPATH
. I do set PYTHONHOME
to the root of the python installation so that I can add it to my system PATH
environment variable so that I can run python from any where.
You don't have to set either of them. PYTHONPATH can be set to point to additional directories with private libraries in them. If PYTHONHOME is not set, Python defaults to using the directory where python.exe was found, so that dir should be in PATH.
For most installations, you should not set these variables since they are not needed for Python to run. Python knows where to find its standard library.
The only reason to set PYTHONPATH is to maintain directories of custom Python libraries that you do not want to install in the global default location (ie, the site-packages
directory).
Make sure to read: http://docs.python.org/using/cmdline.html#environment-variables
Here is what I learned: PYTHONPATH is a directory to add to the Python import search path "sys.path", which is made up of current dir. CWD, PYTHONPATH, standard and shared library, and customer library. For example:
% python3 -c "import sys;print(sys.path)"
['',
'/home/username/Documents/DjangoTutorial/mySite',
'/usr/lib/python3.6', '/usr/lib/python3.6/lib-dynload',
'/usr/local/lib/python3.6/dist-packages', '/usr/lib/python3/dist-packages']
where the first path '' denotes the current dir., the 2nd path is via
%export PYTHONPATH=/home/username/Documents/DjangoTutorial/mySite
which can be added to ~/.bashrc to make it permanent, and the rest are Python standard and dynamic shared library plus third-party library such as django.
As said not to mess with PYTHONHOME, even setting it to '' or 'None' will cause python3 shell to stop working:
% export PYTHONHOME=''
% python3
Fatal Python error: Py_Initialize: Unable to get the locale encoding
ModuleNotFoundError: No module named 'encodings'
Current thread 0x00007f18a44ff740 (most recent call first):
Aborted (core dumped)
Note that if you start a Python script, the CWD will be the script's directory. For example:
username@bud:~/Documents/DjangoTutorial% python3 mySite/manage.py runserver
==== Printing sys.path ====
/home/username/Documents/DjangoTutorial/mySite # CWD is where manage.py resides
/usr/lib/python3.6
/usr/lib/python3.6/lib-dynload
/usr/local/lib/python3.6/dist-packages
/usr/lib/python3/dist-packages
You can also append a path to sys.path at run-time: Suppose you have a file Fibonacci.py in ~/Documents/Python directory:
username@bud:~/Documents/DjangoTutorial% python3
>>> sys.path.append("/home/username/Documents")
>>> print(sys.path)
['', '/usr/lib/python3.6', '/usr/lib/python3.6/lib-dynload',
'/usr/local/lib/python3.6/dist-packages', '/usr/lib/python3/dist-packages',
'/home/username/Documents']
>>> from Python import Fibonacci as fibo
or via
% PYTHONPATH=/home/username/Documents:$PYTHONPATH
% python3
>>> print(sys.path)
['',
'/home/username/Documents', '/home/username/Documents/DjangoTutorial/mySite',
'/usr/lib/python3.6', '/usr/lib/python3.6/lib-dynload',
'/usr/local/lib/python3.6/dist-packages', '/usr/lib/python3/dist-packages']
>>> from Python import Fibonacci as fibo
A little bit less 'ad hoc' solution than directly manipulating the PYTHONPATH
exists with the use of the flag -e
with the pip
command, and allows to seamlessly install local libraries that can be imported, and re-imported to reflect changes made.
In order to be able to import mypackage
the same way you do with any other module, the correct approach is to use pip locally:
python -m pip install -e /path_to_package/mypackage/
python -m
ensures you are using the pip package from the same python
installation you are currently using.
-e
makes it editable, i/e import mypackage
will reload after you make some changes, instead of using the cached one.
mypackage
must be an installable package, i/e contain an __init__.py
file, and a basic setup.py
(or pyproject.toml
file for pipenv
)
minimal setup.py
from setuptools import find_packages, setup
setup(
name='mypackage', # Required
version='0.0.1', # Required
packages=find_packages(), # Required
)
the package structure must be like this:
mypackage/
setup.py
mypackage/ <----- this is a folder inside the other `mypackage/` folder
__init__.py
or as a tree:
└── python_perso folder
└── mypackage folder
├── mypackage folder
│ └── __init__.py
└── setup.py
[edit] after installation, the directory will look like this:
(for a package named mypackage
)
└── python_perso
└── mypackage
├── mypackage
│ ├── __init__.py
│ └── __pycache__
│ └── __init__.cpython-38.pyc
├── mypackage.egg-info
│ ├── PKG-INFO
│ ├── SOURCES.txt
│ ├── dependency_links.txt
│ └── top_level.txt
└── setup.py
5 directories, 7 files
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