Python

# Install virtualenv
pip install virtualenv
 
# Use virtualenv
cd my_project_folder
 
virtualenv venv
#or
virtualenv -p /usr/bin/python2.7 venv
#or
virtualenv -p /usr/bin/python3 venv
 
source venv/bin/activate
 
# Save requirements
pip freeze > requirements.txt
 
# Install requirements
pip install -r requirements.txt

http://docs.python-guide.org/en/latest/dev/virtualenvs/