In this chapter, we will use virtualenv to isolate the environment we will work in. As the name indicates, virtualenv is a tool that creates a virtual environment. It can keep the dependencies required by different projects in separate places while keeping the global site-packages clean. In other words, when you install Flask in the virtual environment, it is only installed in the local virtualenv project directory, not the global site-packages. This make porting the code to other places very easy.
The chances are high that you may have already come across virtualenv while working with Python before, so we will run through this process quickly. If you have not, feel free to pick up one of many excellent tutorials online, such as http://docs.python-guide.org/en/latest/dev/virtualenvs/.
To use , we will first need to install virtualenv:
# Python 3
$ sudo apt...
