Let's initialize virtualenv for our project as follows:

$ virtualenv env

The extra env tells virtualenv to store all the packages into a folder named env. virtualenv requires you to start it before it will sandbox your project:

$ source env/bin/activate
# Your prompt should now look like
(env) $

The source command tells Bash to run the script env/bin/activate in the context of the current directory. Let's reinstall Flask in our new sandbox as follows:

# you won't need sudo anymore
(env) $ pip install flask
# To return to the global Python
(env) $ deactivate

However, it goes against the best practices in Git to track what you don't own, so we should avoid tracking the changes in third-party packages. To ignore specific files in our project, the gitignore file is needed.

$ touch .gitignore

touch is the Bash command to create files, and the dot at the start of a file tells Bash to not list its existence unless specifically told to show hidden files. We will create the simple gitignore file for now:

env/
*.pyc

This tells Git to ignore the entire env directory and ignore all the files that end with .pyc (a compiled Python file). When used in this way, the * character is called a wildcard.