Travis special requirements for each python version
Question: I need unittest2 and importlib for python 2.6 that is not required for other
python versions that travis tests against.

Is there a way to tell Travis-CI to have different requirements.txt files for
each python version?


Answer: Travis CI adds an environment variable called `$TRAVIS_PYTHON_VERSION` that
can be referenced in your .travis.yml:

    
    
    python:
      - 2.6
      - 2.7
      - 3.2
      - 3.3
      - pypy
    install:
      - if [[ $TRAVIS_PYTHON_VERSION == 2.6 ]]; then pip install importlib unittest2; fi
      - pip install -r requirements.txt
    

This would cause `unittest2` and `importlib` to be installed only for Python
2.6, with requirements.txt being installed for all versions listed. You can do
as many of these checks as necessary. Tornado's
[.travis.yml](https://github.com/facebook/tornado/blob/master/.travis.yml)
file uses it quite a bit.

