Your project’s circle.yml

In order for tox to have the versions of python you want available, set them using pyenv local

dependencies:
  override:
    - pip install tox tox-pyenv
    - pyenv local 2.7.9 3.4.3 3.5.0

The versions passed to pyenv local must be installed for this to work. See CircleCI Preinstalled Python Versions for a list.

Corresponding tox.ini

[tox]
envlist = py27,py34,py35

The result of the setup above means running tox will run tests against python 2.7.9, python 3.4.3 and python 3.5.0, assuming those versions of python have been pyenv installed.

notes

If you want tox to exclusively use pyenv which to find executables, you will need use the --tox-pyenv-no-fallback command line option, or set tox_pyenv_fallback=False in your tox.ini. By default, if tox-pyenv fails to find a python executable it will fallback to tox’s built-in strategy.

CircleCI Preinstalled Python Versions

Here is the list of python versions that are pre-installed in the CircleCI build environment (as of 09/27/2017):

$ pyenv versions
  system
  2.6.6
  2.6.8
  2.7
  2.7.10
  2.7.11
  2.7.3
  2.7.4
  2.7.5
  2.7.6
  2.7.7
  2.7.8
* 2.7.9 (set by /home/ubuntu/.pyenv/version)
  3.1.5
  3.2
  3.2.5
  3.3.0
  3.3.2
  3.3.3
  3.4.0
  3.4.1
  3.4.2
  3.4.3
  3.5.0
  pypy-2.2.1
  pypy-2.3.1
  pypy-2.4.0
  pypy-2.5.0

If the version you need isn’t in the list, such as Python 3.6-dev include an install step:

dependencies:
  override:
    - pip install tox tox-pyenv
    - pyenv install --skip-existing 3.6-dev
    - pyenv local 3.6-dev