Example of a .travis.yml with addons, several stages, and PyPI deploy

.travis.yml

os: linux
dist: xenial
language: python
python: 3.7
addons:
  apt:
    sources:
      - sourceline: 'ppa:ubuntugis/ppa'
    packages:
      - gdal-bin
      - geographiclib-tools
      - libfftw3-dev
      - libgdal-dev
      - libgeographic-dev
  homebrew:
    packages:
      # GDAL is already included on osx images
      - geographiclib
      - fftw

install:
  - |
    if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then
        # Work in a virtual environment to avoid having to do
        # "pip3 install --user"
        python3 -m venv venv
        source venv/bin/activate
    fi
  - pip install -e ".[test]"

script: pytest tests

jobs:
  include:
    - stage: formatting
      name: black
      install:
        - pip install black
      script:
        - black --check .
    - stage: formatting
      name: isort
      install:
        - pip install "isort[pyproject]"
      script:
        - isort --check-only

    - stage: packaging
      name: "Python sdist installation"
      install: skip
      script:
        - python setup.py sdist
        - pip install dist/*.tar.gz

    - stage: test
    - stage: test
      os: osx
      # The default osx image (xcode9.4 as of 2019-09-30) has a very old brew,
      # which crashes with the `addons` feature, so we use a non-default more recent one
      # (see https://github.com/Homebrew/homebrew-bundle/issues/540#issuecomment-518301382)
      osx_image: xcode10.2
      language: generic


    - stage: deploy
      if: repo = glostis/plyflatten  # remove and uncomment line below to only deploy on tags
      # if: tag IS present AND repo = glostis/s2p
      install: skip
      script: skip
      deploy:
        - provider: pypi
          user: glostis
          password:
            secure: ""
          distributions: sdist
          server: https://test.pypi.org/legacy/  # remove to deploy on real PyPI
          on:
            branch: develop  # remove and uncomment line below to only deploy on tags
            # tags: true