How do i reverse a string in python using lists and pop()

Question

I am writing a function to take a string and reverse it. I can't work out why my code is returning a reversed string but with only half of the letters of the string passed to it.

   def reverse(text):
        temp = []
        reverse_text = ""
        for i in text:
            temp.append(i)
        for i in temp:
            reverse_text += temp.pop()
        print reverse_text

You are modifying the list while you are iterating over it **with a for loop**. This will almost always get you in trouble. — Jasper, Nov 14 '15 at 10:45
See this: http://stackoverflow.com/questions/6260089/strange-result-when-removing-item-from-a-list — devautor, Nov 14 '15 at 10:59

Jasper · Accepted Answer · 2015-11-14T10:53:41.277

4

I'm not going to post a complete answer, but:

Don't modify a list you're iterating over with a for loop. Bad things will happen (you already realized that)
You therefore can use a while loop to accomplish the task.
You can also use a for loop, but then you'll end up with for i in range(len(temp)): (see other answers), and the range(len(..)) construct is rather "unpythonic".

edited Nov 14 '15 at 10:53

answered Nov 14 '15 at 10:50

Jasper

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score 1 · Answer 2 · answered Nov 14 '15 at 10:46

1

def reverse(text)
    return text[::-1]

answered Nov 14 '15 at 10:46

Petar Ivanov

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score 0 · Answer 3 · answered Nov 14 '15 at 10:46

0

I would just use reversedString = string[::-1], most easy way I think.

answered Nov 14 '15 at 10:46

Tenzin

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Oh wow, they want more code while it could be done so simple? :-( – Tenzin Nov 14 '15 at 10:47
2

yeah.. but someone had to write the code behind [::-1] ;) – shfury Nov 14 '15 at 10:49

aristotll · Answer 4 · 2015-11-14T10:51:37.530

0

for i in range(len(text)):
    reverse_text += temp.pop()

don't change the string.

edited Nov 14 '15 at 10:51

answered Nov 14 '15 at 10:50

aristotll

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score 0 · Answer 5 · answered Nov 14 '15 at 10:50

Every time you are doing pop operation you are changing the temp over which you are iterating as well.

A simple way would be to just do pop n times where n is the length of temp

def reverse(text):
    temp = []
    reverse_text = ""
    for i in text:
        temp.append(i)
    print temp
    for i in range(len(temp)):
#         print i, temp[i]
        reverse_text += temp.pop()
    print reverse_text

score 0 · Answer 6 · answered Nov 14 '15 at 11:08

0

If you can't do:

text[::-1]

Try doing a for loop:

text = 'Hello'
product=''
for x in range(len(text)-1, -1, -1):
    product+=text[x]
return product

answered Nov 14 '15 at 11:08

Chris Nguyen

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How do i reverse a string in python using lists and pop()

6 Answers6