Reverse a string without using build in method [::-1] in Python

If you are new to Python and you don’t know how to reverse a string in Python, here is a sample script using default reverse method [::-1]:

print ("Enter a String")
mystr = input()
#reverse using [::-1]
revstr = mystr[::-1]
print ("Reverse is: "+revstr)

The output of the above program:

Enter a String
superman
Reverse is: namrepus

So basically using [::-1], it is possible to reverse a string, but in interviews, sometimes to test your logical programming skill they may ask you to write a program to reverse a string without using the default reverse method.

The solution for the above question is to write a custom reverse() function in Python.

Here is the solution:

def reverse(InputStr):

    #find the length of the string
    #then subtract by 1, because
    #we all know array starts with 0

    i = len(InputStr) - 1
    rev = ''

    #now loop through each character
    #and then store each character in
    #a new variable rev and return
    
    while  i >= 0:
        rev = rev + str(InputStr[i])
        i = i - 1
    return rev

#here is the usage of the above function
print (reverse('spiderman'))

The above code is well commented, read them to understand.
Are you a Python web developer?, you may need this script!!

This is the Python web script version of reversing a string without using default method:

#!/usr/bin/python
print "Content-type: text/html\n\n";

# Import modules for CGI handling 
import cgi, cgitb 

# Create instance of FieldStorage 
form = cgi.FieldStorage() 

#custom reverse function
def reverse(InputStr):

    i = len(InputStr) - 1
    rev = ''
    
    while  i >= 0:
        rev = rev + str(InputStr[i])
        i = i - 1
    return rev

#get the string from form and store it in mystring
mystring = form.getvalue('string')


print '''
<html>
<body>
    <h3>Web Based Python script to Reverse a string without using default reverse method [::-1]</h3>
    <form action="" method="post">
        <label>Enter a word or a sentence<label>
        <input type="text" name="string" />
        <input type="submit" value="Submit" />
    </form>
</body>
</html>
 
'''
#print only if form is submitted
if(mystring):
	print "<p>Reverse is: <strong>" + reverse(mystring) + "</strong></p>"

The same custom reverse() function is used in the Python web script also, read the comments to understand the other features in the above script such is submitting a form, storing the form value in a variable, calling a function etc.,

And finally the demo of the web script,