How it works...

So far, we have used pip3 install flask multiple times. As the name suggests, the command refers to the installation of Flask, just like any Python package. If we look a bit deeper into the process of installing Flask via pip3, we will see that a number of packages are installed. The following is an outline of the package installation process of Flask:

    $ pip3 install -U flask
    Downloading/unpacking flask
    ...........
    ...........
    Many more lines.........
    ...........
    Successfully installed flask Werkzeug Jinja2 itsdangerous
    markupsafe click
    Cleaning up...
  

If we look carefully at the preceding snippet, we will see that there are six packages installed in total; namely, flask, Werkzeug, Jinja2, click, itsdangerous, and markupsafe. These are the packages on which Flask depends, and it will not work if any of them are missing.