Python venv¶
venv is one of multiple
Python virtual environment managers.
venv is a Python-only environment manager
and is an official Python library.
First, the common workflow for using a venv is described:
- how to create a virtual environment
- how to activate a virtual environment
- how to deactivate a virtual environment
Then:
Create a virtual environment¶
A virtual environment can be created in multiple ways, for example, from scratch, which is not recommended.
Here we discuss the recommended way to create a virtual environment, which has these steps:
- Load a Python module or a modules with Python packages
- Create the virtual environment
1. Load a Python module or a modules with Python packages¶
The first step is described at 'Loading Python' and 'Loading Python package modules'.
Just show me how to do this
Sure, here is how to load a Python module:
Here is how to load a Python package module:
Because you can load Python modules of different Python versions,
you can create venv virtual environments with different Python versions.
Consider adding this in the venv name, e.g. my_python2_venv or my_python3_venv.
2. Create the virtual environment¶
After loading the needed Python modules, one can create a virtual environment most efficiently using:
where [path] is the path where you want to create your venv virtual
environment and [venv_name] is the name of the venv virtual environment.
For example python -m venv --system-site-packages ~/my_venvs/example_venv.
Create virtual environments in your project storage
Virtual environments can take up a lot of disc space.
If you use either (1) many venv virtual environments,
or (2) install many Python packages to a venv virtual environment,
we strongly recommend that you create the venv
virtual environments in your project (/proj/[your_uppmax_project]) folder.
The -m flag makes sure that you use the libraries
from the Python version you are using.
The --system-site-packages flags ensure you use
the packages already installed in the
loaded Python module.
How long does this step take?
This depends.
This takes around 10 seconds:
This takes around 10 seconds:
Activate a virtual environment¶
To activate your newly created virtual environment locate the
script called activate and execute it:
where [path] is the path where you want to create your venv virtual
environment and [venv_name] is the name of the venv virtual environment.
For example source ~/my_venvs/example_venv/bin/activate.
When a venv virtual environment is active,
the prompt is changed to start with the name of your venv.
How does that look like?
This is how your changed prompt looks like:
With the venv virtual environment active,
you can now install and update Python packages
in an isolated way.
Deactivate a virtual environment¶
To deactivate a venv virtual environment:
As the venv virtual environment you just used is now inactive,
the prompt will not show the name of your venv anymore.
You will need to activate a virtual environment to work with it again.
Export and import a virtual environment¶
Export¶
To export the Python packages used in your virtual environment, do:
This will create a file with all the Python packages and their versions, using the conventional name for such a file.
How does that file look like?
This is how a requirements.txt file may look like:
anndata==0.10.5.post1
anyio==4.2.0
appdirs==1.4.4
argon2-cffi==23.1.0
argon2-cffi-bindings==21.2.0
[more Python packages]
websocket-client==1.7.0
Werkzeug==3.0.1
widgetsnbextension==4.0.9
zipp==3.17.0
zope.interface==6.1
Note that [more Python packages] is a placeholder for many
more Python packages.