I wrote the python exercise myself.

String, shaping, floating-point, tuple elements (characters) of the index is immutable, cannot change is that you can use the variable name with square brackets, and then filled in square brackets inside the index value of the string, the index value is zero-based, and the list of words inside the element index value can be arbitrarily assigned value

When the slice has a step, the opening end is contained within it and is intercepted. But what if the slices have no stride size?   The beginning contains the end not to contain. Next look at the example

A = "abcdef"//String

b = "123456789"

c = a[0] * 20

I wrote the python exercise myself.