## Virtualenv is a tool that creates isolated Python development environments on your computer.
So why is this useful? Say you see a Python library that you want to try out. If you installed this library systemwide, you run the risk of messing up other libraries you've installed. Instead, you can use virtualenv to first create an isolated environment and then safely install the library inside this environment without affecting the rest of your computer.
You can then keep this virtual environment around for more development work or simply delete it when you're finished trying it out. Either way, your system remains organized and clutter-free.
### To install virtualenv, type:
`pip install virtualenv`
### Once you're inside your project folder, type the command:
`virtualenv venv`
Virtualenv is creating a new folder named **venv** that contains a fresh copy of Python and the package installer pip. Once you've done this, activate your new virtual environment so you can begin working inside of it.
### Type:
`source venv/bin/activate`
You can see that we're inside the isolated environment because of the **venv** that shows up in front of the prompt. Now that we're inside the isolated environment, we can safely install Flask without affecting the rest of the computer.