virtualenv-multiver

virtualenv-multiver is a wrapper around virtualenv, the standard tool for creating isolated Python environments. It's built to allow multiple versions of Python to be usable within a single environment. This is really handy when you're doing development and testing across a range of Python versions, and you don't want to have to juggle your active environment for every version.

It also comes with a handy tool called pydo, which can run a Python/Pip command across a range of Python versions.

Installation

Simple:

$ pip install virtualenv-multiver

Virtualenv Usage

Also simple. To create a new virtual environment, just provide the path to that environment and the versions you want installed. For example:

$ virtualenv-multiver ~/venvs/my-project 2.7 3.8-3.11

Or for pypy:

$ virtualenv-multiver ~/venvs/my-project pypy pypy3

The resulting virtual environment will include all those versions of Python without any additional configuration.

pydo Usage

pydo can run a command across a range of Python versions. It looks for a commandX.Y or command-X.Y that it can run for the provided command and for each version of Python.

Usage:

$ pydo [<version> [<version> ...]] <command>

Versions are in X.Y form, and can include ranges like 3.8-3.10.

For example:

$ pydo 2.7 3.6 3.8-3.10 pip install -e .

This will automatically run:

$ python2.7 -m pip install -e .
$ python3.6 -m pip install -e .
$ python3.8 -m pip install -e .
$ python3.9 -m pip install -e .
$ python3.10 -m pip install -e .

If you don't specify any versions, the Python versions available in the virtualenv-multiver environment will be used.

You can also configure the list of default versions in .pydorc, pyproject.toml, or setup.cfg.

Configuring pydo

pydo first checks for a $VIRTUAL_ENV/.pydorc file.

If not found, it will check in the current directory and all parent directories for each of these files:

• .pydorc
• pyproject.toml
• setup.cfg

.pydorc

pydo first checks for a .pydorc file. One is automatically generated in your virtualenv-multiver environment (for environments created using virtualenv-multiver 2.1 or higher).

Format:

[pydo]
pyvers=<version>[, <version>, ...]

For example:

[pydo]
pyvers=2.7,3.8-3.11

pyproject.toml

pydo next checks for a pyproject.toml file. This requires toml support in your Python environment.

Format:

[tool.pydo]
pyvers = [<version>, ...]

For example:

[tool.pydo]
pyvers = ["2.7", "3.8-3.11"]

setup.cfg

pydo finally checks for a setup.cfg file.

Format:

[pydo]
pyvers=<version>[, <version>, ...]

For example:

[pydo]
pyvers=2.7,3.8-3.11

FAQ

How does virtualenv-multiver work?

virtualenv-multiver runs through the list of Python versions provided and calls out to virtualenv for each version

After each virtualenv call, it fixes up the tree a bit. This involves:

• Ensuring symlinks point to the right place (python2 points to the latest python2.* specified, for instance)
• Patching any installed scripts (such as pip3.8) and making sure it points to the correct, versioned interpreter
• Moves and patches some binaries and configuration files around to avoid collision issues.

Once done, it sets the top-level symlinks for python2, python3, pip2, pip3, etc. (any that specify a major version) to point to the latest version in that series.

It then sets the generic, version-less ones (python, pip, etc.) to point to the Python 2 versions (if Python 2 is installed), or Python 3 (if not). This helps ensure compatibility with scripts that expect python to mean "Python 2".

Are all versions of CPython supported?

Yes. Pretty much. It depends on whether virtualenv itself will support the version.

Is PyPY supported?

Yes. Sorta.

PyPy doesn't cleanly install alongside CPython in a virtual environment, due to CPython and PyPy claiming some of the same files and directories. We only allow PyPy to install independently or alongside another PyPy.

You may have issues even with multiple PyPy installations. They'll install and run, but will share the same site-packages directory, which is beyond our control for the moment.

If this isn't a problem for you, go for it. Otherwise, you may want to stick to a standard virtualenv call for those.

How do I report a bug?

You can file an issue on the GitHub issue tracker.

Who uses this?

We use virtualenv-multiver at Beanbag for our Review Board and RBCommons products.

If you use this, let us know and we'll add you to a list here!

What else do you build?

Lots of things. Check out some of our other open source projects.