Reverse a string without using reversed() or [::-1]?

Question

I came across a strange Codecademy exercise that required a function that would take a string as input and return it in reverse order. The only problem was you could not use

Answer 1

Only been coding Python for a few days, but I feel like this was a fairly clean solution. Create an empty list, loop through each letter in the string and append it to the front of the list, return the joined list as a string.

def reverse(text):
backwardstext = []
for letter in text:
    backwardstext.insert(0, letter)
return ''.join(backwardstext)

Answer 2

I used this:

def reverse(text):
s=""
l=len(text)
for i in range(l):
    s+=text[l-1-i]
return s

Answer 3

I have also just solved the coresponding exercise on codeacademy and wanted to compare my approach to others. I have not found the solution I used so far, so I thought that I sign up here and provide my solution to others. And maybe I get a suggestion or a helpful comment on how to improve the code.

Ok here it goes, I did not use any list to store the string, instead I have just accessed the string index. It took me a bit at first to deal with the len() and index number, but in the end it worked :).

def reverse(x):
reversestring = ""
for n in range(len(str(x))-1,-1, -1):
    reversestring += x[n]
return reversestring 

I am still wondering if the reversestring = "" could be solved in a more elegant way, or if it is "bad style" even, but i couldn't find an answer so far.

Answer 4

This is my solution using the for i in range loop:

def reverse(string):
    tmp = ""
    for i in range(1,len(string)+1):
        tmp += string[len(string)-i]            
    return tmp

It's pretty easy to understand. I start from 1 to avoid index out of bound.

Answer 5

The way I can think of without using any built-in functions:

a = 'word'
count = 0
for letter in a:
    count += 1

b = ''
for letter in a:
    b += a[count-1]
    count -= 1

And if you print b:

print b
drow

Answer 6

I created different versions of how to reverse a string in python in my repo: https://github.com/fedmich/Python-Codes/tree/master/Reverse%20a%20String

You can do it by using list-comprehension or lambda technique:

# Reverse a string without using reverse() function
s = 'Federico';
li = list( s )  #convert string to list

ret = [ li[i-1] for i in xrange(len(li),0,-1)  ]    #1 liner lambda
print ( "".join( ret ) )

or by doing a backward for loop

# Reverse a string without using reverse() function
s = 'Federico';
r = []

length = len(s)
for i in xrange(length,0,-1):
    r.append( s[ i - 1] )

print ( "".join(r) )