A string is iterable, meaning it has an index that starts at
0 and goes up to the string length minus 1 (because of zero-indexing).
In Python, the first character of a string is at index 0
my_string = "some characters in a string"
my_string # -> 's'
The last character may be found in one of two ways, via the index,
my_string[len(my_string) - 1] # -> 'g'
or by negative indexing,
my_string[-1] # -> 'g'
The negative sign tells Python to start on the right side and count to the left starting outside the string.
-1 is the first index from the right. By this we can conclude that the first character, negative indexed would be,
my_string[-len(my_string)] # -> 's'