virtualenvwrapper

If you use Python heavily you will likely be familiar with Virtual Environments. These provide isolated installs of specific packages that take precedence over any packages installed at the system level. There are lots of tools and frameworks for working with virtual environments such as venv, virtualenv and Conda. This post introduces and shows some of the features of virtualenvwrapper.

Clouds Rising at Sunset by Me

virtualenvwrapper

virtualenvwrapper is…

a set of extensions to Ian Bicking’s virtualenv tool. The extensions include wrappers for creating and deleting virtual environments and otherwise managing your development workflow, making it easier to work on more than one project at a time without introducing conflicts in their dependencies.

It has the following main features…

1. Organizes all of your virtual environments in one place.
2. Wrappers for managing your virtual environments (create, delete, copy).
3. Use a single command to switch between environments.
4. Tab completion for commands that take a virtual environment as argument.
5. User-configurable hooks for all operations (see Per-User Customization).
6. Plugin system for creating more sharable extensions (see Extending Virtualenvwrapper).

Installation

Many systems have virtualenvwrapper available in their package manager.

emerge -av virtualenvwrapper          # Gentoo
pacman -Syu python-virtualenvwrapper  # Arch
apt-get install virtualenvwrapper     # Debian

Once installed you need to set two key variables $WORKON_HOME and $PROJECT_HOME and ensure the virtualenvwrapper.sh is sourced on starting a shell. $WORKON_HOME is where your virtual environments will be created and stored, whilst $PROJECT_HOME is where projects will be created if you choose to use the helper functions for making projects. Set these to what you want, my options are below. To find out where virtualenvwrapper.sh is installed on your system use which virtualenvwrapper.sh. Once you’ve decided substitute the values in the following of your .bashrc (Bash)or .zshrc (ZSH) depending on which shell you use.

export WORKON_HOME=${HOME}/.virtualenvs
export PROJECT_HOME=${HOME}/work/git/
source /usr/bin/virtualenvwrapper.sh

Creating a Virtual Environment

This is straight-forward.

mkvirtualenv <env_name>

postmkvirtualenv

But what if there are some tools that you want to install each and every time you create a virtual environment, regardless of the project you are working on? For example I use the jedi-language-server and want to have various packages such as ipython, pytest and various extensions, linters such as ruff and pylint available by default in every environment you create. Fortunately there is a simple hook that can be run after the creation of a new environment. The file ~/.virtualenvs/postmkvirtualenv is sourced and run after having run mkvirtualenv and so any commands in there are executed as it is essentially a Bash script.

If you maintain a dotfiles directory and have a file that lists the packages you want installed under ~/dotfiles/python/venv_minimal_requirements.txt then you can have the files listed here installed when creating a new virtual environment by appending the command pip install -r ~/dotfiles/python/venv_minimal_requirements.txt to the ~/.virtualenvs/postmkvirtualenv file.

echo "pip install -r ~/dotfiles/python/venv_minimal_requirements.txt" >> ~/.virtualenvs/postmkvirtualenv

Project Directories

Typically code for a project resides in its own directory and this can be automatically bound to the virtual environment using the mkproject command instead of mkvirtualenv. The project directory is stored in the $PROJECT_HOME path you will have configured during installation. You can then create a project and a virtual environment with…

mkproject new_project

Switching to Project Directories

You can switch to a projects directory automatically on activating a particular virtual environment using setvirtualenvproject from the project directory when a specific environment is activated. Make sure you are in the project directory for the corresponding project!. It adds an entry to the ~/.virtualenv/<env_name>/.project file that reflects the directory associated with the environment. Then when you activate the directory via workon <env_name> it will automatically change to the project directory.

Deactivating and Removing Virtual Environments

Its straight-forward to deactivate the current virtual environment just type deactivate. Similarly you can remove a virtual environment with rmvirtualenv <env_name>.

One neat option if you want to keep a virtual environment but install all packages anew is the ability to remove all third-party packages in the current virtual environment using wipeenv.

Temporary Virtual Environments

Sometimes you just want to try something out quickly in a clean Virtual Environment, if for example you are reviewing a Pull Request. virtualenvwrapper can help here as it has the mktmpenv. There are two options here -c|--cd or -n|--no-cd which changes directory post-activation or doesn’t respectively. The environment gets a unique name and will be deleted automatically when it is deactivated.

Drawbacks

There are a couple of drawbacks I’ve found to using using virtualenvwrapper.

The first is that mkproject doesn’t allow nesting of project directories, you have to specify a single directory and it will be created under the $PROJECT_HOME directory with the associated environment name. This doesn’t work for me as I use the structure ~/work/git as the base but then have sub-directories based on the Git Forge (GitHub/GitLab/Codeberg) the repository is associated with and further nesting to reflect the user/organisation within as I have both a personal and work accounts. E.g. ~/work/git/hub/ns-rse/ns-rse.github.io which is the source for this site and associated with my work account (ns-rse) or ~/work/git/lab/nshephard/tcx2gpx which is a project of mine (tcx2gpx) hosted on GitLab. This means that if I wanted to create a project with mkproject based on $PROJECT_HOME being /work/git following this structure I would specify mkproject git/lab/new_project and whilst the directory is created, the virtual environment is created as git/lab/new_project which is truncated to git and you can’t workon git because the activation scripts are nested deeper under git/lab/new_project. Further each environment I created would then conflict. I could probably work around this by creating symbolic links but in practice I just use mkvirtualenv and setvirtualenvproject after I git clone work.

This is a problem specifically of my own creation though, something other users might find causes greater friction is that virtualenvwrapper doesn’t support creating and keeping the virtual environments within the project directory itself. This is never something that I’ve wanted to do myself though as I find it tidier to keep them all in one place and easier to find and remove obsolete environments.

Conclusion

I’ve used virtualenvwrapper for years and its a nice light-weight alternative to other solutions of using Pythons Virtual Environments such as venv or Conda. It has some limitations but its worth giving it a whirl as there are lots of useful helper functions and hooks that smooth the process of creating, using and switching between virtual environments.

Links

• virtualenvwrapper documentation