Speed up Python and Node.js builds on Travis CI

Travis CI's caching archives all directories listed in the configuration and uploads them to Amazon S3. Cached contents are available to any build on the repository, including Pull Requests. For Python and Node.js projects, you could cache both site-packages and node_modules directories in every Travis CI build.

Here is an example of .travis.yml:

sudo: false

language: python

python:
  - "2.7"

node_js: 4

cache:
  directories:
    - $HOME/.cache/pip
    - $HOME/virtualenv/python2.7.9/lib/python2.7/site-packages
    - node_modules

before_install:
  - pip install -U pip

install:
  - pip install -r requirements.txt
  - pip install coverage --ignore-installed
  - npm install

script:
  - coverage run manage.py test

In the case of mine, after applying these changes, the installation time of pip and npm reduces from 180 seconds to 5 seconds.

One thing should be mentioned here: Since we didn't specify any bin folder in the configuration (and I don't think that's necessary), any execution file that being installed by pip such as coverage or django-admin.py will not exist in subsequent builds. If you need those commands, you could just force install them by adding pip install some_package --ignore-installed.

References:

Caching Dependencies and Directories
https://docs.travis-ci.com/user/caching/

How to cache requirements for a Django project on Travis-CI?
http://stackoverflow.com/questions/19422229/how-to-cache-requirements-for-a-django-project-on-travis-ci

如何在 Travis CI 加快 Python 單元測試速度
https://tzangms.com/how-to-speed-up-python-unit-test-on-travis-ci/