Reverse a Python string without omitting start and end slice

Question

How do you reverse a Python string without omitting the start and end slice arguments?

word = "hello"
reversed_word = word[::-1]

I understand that this works, but how would I get the result by specifying the start and end indexes?

word = "hello"
reversed_word = word[?:?:-1]

It's hard to explain to students why word[::-1] reverses a string. It's better if I can give them logical reasoning rather than "it's the pythonic way".

The way I explain word[::1] is as follows: "You have not specified the start so it just starts from the start. You have not specified the end so it just goes until the end. Now the step is 1 so it just goes from the start to the end 1 character by 1." Now when my students see word[::-1] they are going to think "We have not specified the start or the end so it will go through the string -1 characters at a time?"

Answer 1

Some other ways to reverse a string:

word = "hello"
reversed_word1 = word[-1: :-1] 
reversed_word2 = word[len(word)-1: :-1]   
reversed_word3 = word[:-len(word)-1 :-1]    

One thing you should note about the slicing notation a[i:j:k] is that omitting i and j doesn't always mean that i will become 0 and j will become len(s). It depends upon the sign of k. By default k is +1.

• If k is +ve then the default value of i is 0 (start from the beginning). If it is -ve then the default value of i is -1 (start from the end).
• If k is +ve then the default value of j is len(s) (stop at the end). If it is -ve then the default value of j is -(len(s)+1) (stop at the beginning).

Now you can explain your students how Hello[::-1] prints olleH.