The colons (:) in subscript notation (iterable[subscript]) make slice notation - which has the optional arguments, start, stop, stride:
string[start:stop:stride]
Python slicing is a computationally fast way to methodically access parts of your data. In my opinion, to be even an intermediate Python programmer, it's one aspect of the language that it is necessary to be familiar with.
Animation are created using Python Manim Community Library
![](https://s2.save4k.ru/pic/adZkGQJLLGA/maxresdefault.jpg)