Building a Python Project

What This Guide Covers

Language versions and other build-environment specific information are in our reference pages:

Python builds are not available on the macOS environment.

The rest of this guide covers configuring Python projects in Travis CI. If you’re new to Travis CI please read our Getting Started and build configuration guides first.

Specifying Python versions

Specify python versions using the python key. As we update the Python build images, aliases like 3.6 will point to different exact versions or patch levels.

language: python
  - "2.6"
  - "2.7"
  - "3.3"
  - "3.4"
  - "3.5"
  - "3.5-dev"  # 3.5 development branch
  - "3.6"
  - "3.6-dev"  # 3.6 development branch
  - "3.7-dev"  # 3.7 development branch
# command to install dependencies
  - pip install -r requirements.txt
# command to run tests
  - pytest # or py.test for Python versions 3.5 and below

Travis CI Uses Isolated virtualenvs

The CI Environment uses separate virtualenv instances for each Python version. This means that as soon as you specify language: python in .travis.yml your tests will run inside a virtualenv (without you having to explicitly create it). System Python is not used and should not be relied on. If you need to install Python packages, do it via pip and not apt.

If you decide to use apt anyway, note that for compatibility reasons, you’ll only be able to use the default Python versions that are available in Ubuntu (e.g. for Trusty, this means 2.7.6 and 3.4.3). To access the packages inside the virtualenv, you will need to specify that it should be created with the --system-site-packages option. To do this, include the following in your .travis.yml:

language: python
  system_site_packages: true

PyPy Support

Travis CI supports PyPy and PyPy3.

To test your project against PyPy, add “pypy” or “pypy3” to the list of Pythons in your .travis.yml:

language: python
  - "2.6"
  - "2.7"
  - "3.4"
  - "3.5"
  - "3.6"
  # PyPy versions
  - "pypy2.7"
  - "pypy3.5"
# command to install dependencies
  - pip install -r requirements.txt
  - pip install .
# command to run tests
script: pytest

Nightly build support

Travis CI supports a special version name nightly, which points to a recent development version of CPython build.

Development releases support

From Python 3.5 and later, Python In Development versions are available.

You can specify these in your builds with 3.5-dev, 3.6-dev, 3.7-dev or 3.8-dev.

Recent Python development branches require OpenSSL 1.0.2+. As this library is not available for Trusty, 3.7-dev, 3.8-dev, and nightly do not work (or use outdated archive).

Default Build Script

Python projects need to provide the script key in their .travis.yml to specify what command to run tests with.

For example, if your project uses pytest:

# command to run tests
script: pytest  # or py.test for Python versions 3.5 and below

if it uses make test instead:

script: make test

If you do not provide a script key in a Python project, Travis CI prints a message (“Please override the script: key in your .travis.yml to run tests.”) and fails the build.

Using Tox as the Build Script

Due to the way Travis is designed, interaction with tox is not straightforward. As described above, Travis already runs tests inside an isolated virtualenv whenever language: python is specified, so please bear that in mind whenever creating more environments with tox. If you would prefer to run tox outside the Travis-created virtualenv, it might be a better idea to use language: generic instead of language: python.

If you’re using tox to test your code against multiple versions of python, you have two options:

  • use language: generic and manually install the python versions you’re interested in before running tox (without the manual installation, tox will only have access to the default Ubuntu python versions - 2.7.6 and 3.4.3 for Trusty)
  • use language: python and a build matrix that uses a different version of python for each branch (you can specify the python version by using the python key). This will ensure the versions you’re interested in are installed and parallelizes your workload.

A good example of a travis.yml that runs tox using a Travis build matrix is twisted/klein.

Dependency Management


By default Travis CI uses pip to manage Python dependencies. If you have a requirements.txt file, Travis CI runs pip install -r requirements.txt during the install phase of the build.

You can manually override this default install phase, for example:

install: pip install --user -r requirements.txt

Please note that the --user option is mandatory if you are not using language: python, since no virtualenv will be created in that case.

Custom Dependency Management

To override the default pip dependency management, alter the before_install step as described in general build configuration guide.

Testing Against Multiple Versions of Dependencies (e.g. Django or Flask)

If you need to test against multiple versions of, say, Django, you can instruct Travis CI to do multiple runs with different sets or values of environment variables.

Use env key in your .travis.yml file, for example:


and then use ENV variable values in your dependencies installation scripts, test cases or test script parameter values. Here we use ENV variable value to instruct pip to install an exact version:

  - pip install -q Django==$DJANGO_VERSION
  - python -q install

The same technique is often used to test projects against multiple databases and so on.

For a real world example, see getsentry/sentry and jpvanhal/flask-split.

Build Matrix

For Python projects, env and python can be given as arrays to construct a build matrix.