How to reverse and concatenate strings at certain indexes?

Question

For my assignment, I'm required to first come up with a function that reverses a string that is inputted (which I've already done using the code below)

def reverse(s):
    if len(s) <= 1:
        return s

    return reverse(s[1:]) + s[0]

The next part is to construct a new string from a given one by breaking it at a certain index value, and concatenating the reverse of the second part (the suffix) to the beginning of the first part (the prefix)

For example, if the input string is 'laptop' and the chosen index value is, say, 3, the string is broken as 'lap' + 'top'. 'top' would then be reversed to 'pot' and would be concatenated with the prefix (in the order) as 'pot' + 'lap'

The assignment is somewhat confusing and since I'm a novice with little to no experience besides a couple of days working in Python, I'm a little confused as to what to do. I'm pretty sure I have to use the slice and concatenation operators but I'm not sure how I should go about constructing a function that suits the above criteria. Any pointers?

score 1 · Answer 1 · edited Jan 29 '15 at 00:06

1

Something like:

def concatreverse(s, i):
    return s[:i] + reverse(s[i:])

edited Jan 29 '15 at 00:06

skrrgwasme

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answered Jan 28 '15 at 23:43

L3viathan

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tenwest · Answer 2 · 2015-01-29T00:01:27.790

1

Combining the other two answers, and implementing your reverse function:

def concatreverse(s, i):
    """This function takes in a string, s, which
    is split at an index, i, reverses the second of the split,
    and concatenates it back on to the first part"""

    #Takes your inputs and processes
    part1,part2 = s[0:i], s[i:]

    #Reverse part2 with the function you already created
    #this assumes it is accessible (in the same file, for instance)
    rev_part2 = reverse(part2)

    #concatenate the result
    result = part1 +rev_part2

    #Give it back to the caller
    return result

As a beginner, it helps to step through line by line, or doing tests using the interpreter to see exactly what's going on :)

edited Jan 29 '15 at 00:01

answered Jan 28 '15 at 23:54

tenwest

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I employed something similar to this into my new function. Thanks for the advice! Explanation is much simpler compared to my instructors. – Abort Mission Jan 29 '15 at 00:10
python is a bit cheap because you can get pretty far without knowing TRULY what's going on, but if you're pursuing computer science, it's probably worth banging your head against their explanations a bit :) you're welcome and good luck! – tenwest Jan 29 '15 at 00:20

score 0 · Answer 3 · answered Jan 28 '15 at 23:43

0

You could do as follows:

s = 'laptop'
i = 3;

# split the string into two parts
part1,part2 = s[0:i], s[i:]

# make new string starting with reversed second part.
s2 = part2[::-1] + part1
print(s2) 
# prints: potlap

answered Jan 28 '15 at 23:43

Marcin

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That makes sense. But wouldn't I have to define the range first? – Abort Mission Jan 28 '15 at 23:49
What ranges? I split by index, as I understand from your question. You can check if index is grater than the length of string though. This would be good. – Marcin Jan 28 '15 at 23:56
Oh, ok. I assumed I would've had to define the range as len(s) or something related to that. – Abort Mission Jan 29 '15 at 00:00
Nah dont need. `[::-1]` this reverses string or any list. Its an alternative to using `reverse.` function. – Marcin Jan 29 '15 at 00:02

How to reverse and concatenate strings at certain indexes?

3 Answers3