Printing a String in Reverse After Extracting

Question

I am trying to create a program in which the user inputs a statement containing two '!' surrounding a string. (example: hello all! this is a test! bye.) I am to grab the string within the two exclamation points, and print it in reverse letter by letter. I have been able to find the start and endpoints that contain the statement, however I am having difficulties creating an index that would cycle through my variable userstring in reverse and print.

test = input('Enter a string with two "!" surrounding portion of the string:')
expoint = test.find('!')
     #print (expoint)
twoexpoint = test.find('!', expoint+1)
     #print (twoexpoint)
userstring = test[expoint+1 : twoexpoint]
     #print(userstring)


number = 0
while number < len(userstring) :
    letter = [twoexpoint - 1]
    print (letter)
    number += 1

What happens if the string has 3 ```!```? – Abhinav Mathur Oct 21 '20 at 18:02 — Abhinav Mathur, Oct 21 '20 at 18:02

ThunderHorn · Answer 1 · 2020-10-21T18:24:52.887

Explanation we use regex to find the pattern then we loop for every occurance and we replace the occurance with the reversed string. We can reverse string in python with mystring[::-1] (works for lists too)

Python re documentation Very usefull and you will need it all the time down the coder road :). happy coding!

Very usefull article Check it out!

import re # I recommend using regex

def reverse_string(a):
    matches = re.findall(r'\!(.*?)\!', a)
    for match in matches:
        print("Match found", match)
        print("Match reversed", match[::-1])
        for i in match[::-1]:
            print(i)

In [3]: reverse_string('test test !test! !123asd!')
Match found test
Match reversed tset
t
s
e
t
Match found 123asd
Match reversed dsa321
d
s
a
3
2
1

@Tomerikoo oups :) now much better fixed it! – ThunderHorn Oct 21 '20 at 18:25 — ThunderHorn, Oct 21 '20 at 18:25

Tomerikoo · Accepted Answer · 2020-10-21T18:25:39.207

twoexpoint - 1 is the last index of the string you need relative to the input string. So what you need is to start from that index and reduce. In your while loop:

letter = test[twoexpoint- number - 1]

Each iteration you increase number which will reduce the index and reverse the string.

But this way you don't actually use the userstring you already found (except for the length...). Instead of caring for indexes, just reverse the userstring:

for letter in userstring[::-1]:
    print(letter)

score -1 · Answer 3 · answered Oct 21 '20 at 18:09

You're overcomplicating it. Don't bother with an index, simply use reversed() on userstring to cycle through the characters themselves:

userstring = test[expoint+1:twoexpoint]
for letter in reversed(userstring):
    print(letter)

Or use a reversed slice:

userstring = test[twoexpoint-1:expoint:-1]
for letter in userstring:
    print(letter)

Printing a String in Reverse After Extracting

3 Answers3