# Install specified python requirements in indicated (virtualenv). - pip: requirements: /my_app/requirements.txt virtualenv: /my_app/venv 
If python3 is really broken, you can specify which version of python you want to use:
 # Install specified python requirements in indicated (virtualenv). - pip: requirements: /my_app/requirements.txt virtualenv: /my_app/venv virtualenv_command: virtualenv-2.7 
I think this answers your question.