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up vote -3 down vote favorite

This question already has an answer here:

I am new to programming. I am trying to write a code to print the reverse of any given string. I have written the following code:

import math
string= raw_input ("Enter string")
n= len(string)
ol= n-1
for ol>-1,ol--:
    print string[ol]

but i am getting syntax error. Please help me to figure this out.

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marked as duplicate by FakeRainBrigand, Ashwini Chaudhary, Lennart Regebro, inspectorG4dget, joaquin Sep 4 '13 at 17:12

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
3  
for ol>-1,ol--, that's not python syntax. –  Ashwini Chaudhary Aug 30 '13 at 6:58
2  
Why do you need math module? –  badc0re Aug 30 '13 at 6:59
1  
@badc0re I said i am new to programming. So i just tried importing it to check if it would work out for me. –  Nelson Menezes Aug 30 '13 at 7:04
1  
People downvoting this question: You were once beginners as well and stumped by similar problems, unable to think yourself out. –  Aaron Digulla Aug 30 '13 at 7:04
1  
Right maybe you are a beginner, but have you tried reading about basics of python? –  badc0re Aug 30 '13 at 7:09

3 Answers 3

up vote 3 down vote accepted

Python tries very hard to present code in a readable way. This means you don't get many of the ugly, hard to understand shortcuts that other languages like C offer. Instead, you get other, much easier to understand shortcuts.

The code to loop over a range in python is:

for ol in range(n):

To iterate backwards, use 

for ol in range(n-1,-1,-1):

But of course, someone couldn't resist and add an unreadable shortcut to the language:

print string[::-1]

Related:

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It worked for me and thanks for the references. –  Nelson Menezes Aug 30 '13 at 7:10
up vote 1 down vote

You can use these links for your further work, i know that this answer is out of the topic:

Code Academy

People all over the world are learning with Codecademy.

Python the hard way

Learn Python The Hard Way, 3rd Edition

Python Monk

Free, interactive tutorials to help you discover Python idioms, in your browser!

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Thank you for the references you provided. Will definitely go through it. –  Nelson Menezes Aug 30 '13 at 7:19
up vote 1 down vote

If you want to code the string reverse yourself, try this as well. This will be useful when you reverse a very large string. You just have to traverse only half of it.

Data = list("ABCDEF")
Len  = len(Data)

for i in range(Len//2):
    Data[i], Data[Len - i - 1] = Data[Len - i - 1], Data[i]

Data = ''.join(Data)

print Data

NOTE: This solution is just for learning. For practical purposes, use @Aaron Digulla's third option. It will give far better performance than anything else. Its called slicing. Read about it here http://docs.python.org/2/tutorial/introduction.html#strings

print string[::-1]
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