tox-interpreters

What?

tox-interpreters enables overriding the logic tox follows in resolving base Python interpreters when it comes to virtual environment creation. It does so by allowing the user to bind test env names to the interpreters of their choice, by means of regular expressions.

Why?

I usually run tox from a permanent and isolated virtual environment, and I keep Python interpreters in multiple versions installed at the system level for tox itself to use whenever it needs to create a test environment.

It turns out that if the required Python version for a new environment matches the one tox is running from, tox will use its own Python interpreter as base to perform the creation, despite its belonging to a virtual environment - the system level interpreter will not be used.

The standard way of fixing this would be by setting basepython to the absolute path of the interpreter to be used for a specific environment. Unfortunately this becomes impractical as soon as a generative envlist with factors is involved.

Of course this is just one of the many possible use cases. Generally speaking, tox-interpreters aims at providing full consistency and flexibility in virtual environment creation across Python versions, by allowing the user to choose the base interpreter to be used depending on the name of the test environment.

Installation

tox-interpreters has been developed as a tox plugin, therefore it has to be installed along with tox itself.

$ pip install tox-interpreters

Usage

To use tox-interpreters, add the setting interpreter to the [testenv] section of your tox configuration file (typically tox.ini), as follows:

[testenv]
interpreter =
    py37.*=/path/to/python3.7
    py38.*=/path/to/python3.8

The interpreter setting accepts a list of <regex>=<interpreter> lines as value. Each line binds a regular expression to an interpreter.

Whenever a new test environment needs to be created, the selection of the base Python interpreter is performed by checking the name of the environment against all the regular expressions, in order. The interpreter bound to the first matching regex will be used.

In case of no match, the selection logic falls back to the standard behaviour of tox - that is, everything works just as if tox-interpreters wasn't installed at all.

Interpreters can be specified by their absolute path or just by their file name. In the latter case, the path to the file needs to be in the PATH environment variable for virtual environment creation to succeed.

[testenv]
interpreter =
    py37.*=/path/to/python3.7
    py38.*=python3.8

License

See: LICENSE