What is Python Whitespace and how does it work?

Whitespace is used to denote blocks. In other languages curly brackets ({ and }) are common. When you indent, it becomes a child of the previous line. In addition to the indentation, the parent also has a colon following it.

im_a_parent:
    im_a_child:
        im_a_grandchild
    im_another_child:
        im_another_grand_child

Off the top of my head, def, if, elif, else, try, except, finally, with, for, while, and class all start blocks. To end a block, you simple outdent, and you will have siblings. In the above im_a_child and im_another_child are siblings.