如何对字符串进行反向切片方法

Question

I have a alphabet string like:

string = 'abcdefghijklmnopqrstuvwxyz'

if want to do slicing and and go from z to a but with 3 steps. what should I do? I know string[::-1] will reverse it but how can I make it go by 3 steps each time?

I have done it by assigning a new string which is reverse of the other string and do slicing with 3 steps from there. I'm looking for a new way to do it without changing the previous string and doing it on the same spot

Answer 1

The last number in the slice is the interval:

string = 'abcdefghijklmnopqrstuvwxyz'
string[::-3]
'zwtqnkheb'

Answer 2

If you want 3 letter slices starting from the end and going backward, you can use a list comprehension:

string = 'abcdefghijklmnopqrstuvwxyz'
slices =  [ string[i:i+3][::-1] for i in range(len(string)-3,0,-3) ]

# ['zyx', 'wvu', 'tsr', 'qpo', 'nml', 'kji', 'hgf', 'edc']