Python3 string slicing

[jakey]

I am trying to learn Python3 and have come across Lists. I know that counting begins at 0 and ends at -1
But i am having some difficulty in understanding the following example:

S[6:1:-2] = A B C D E F G H I

Could someone please explain what is going on here please.

 

[menator01]

That is not valid syntax

#Creates String
S = 'A B C D E F G H I'

# 6 print the sixth character :1 go back one character : -2 Go back two characters from sixth character
print(S[6:1:-2])

Output

DCB

 

[jakey]

Very big thanks menator01 for taking the time out to reply and of course the explanation.