Explore our sites

Stack Exchange
tour help careers 2.0
Take the 2-minute tour ×
Stack Overflow is a question and answer site for professional and enthusiast programmers. It's 100% free, no registration required.
up vote 285 down vote favorite
75

There is no built in reverse function in Python's str object. What is the best way of implementing this?

If supplying a very concise answer, please elaborate on it's efficiency. Is the str converted to a different object, etc.

share|improve this question
2  
Not the best way by far, but one of the many ways to do it if you weren't allowed to use slicing or reversed(), is ''.join((s[i] for i in xrange(len(s)-1, -1, -1))). –  Dennis Mar 6 '13 at 6:49
add comment

2 Answers

up vote 576 down vote accepted

How about:

>>> 'hello world'[::-1]
'dlrow olleh'

This is extended slice syntax. It works by doing [begin:end:step] - by leaving begin and end off and specifying a step of -1, it reverses a string.

share|improve this answer
17  
That's very pythonic. Good job! –  dionyziz Feb 22 '12 at 19:23
9  
@grass: 'hello'[:4][::-1] would do it –  Paolo Bergantino Apr 28 '12 at 16:46
31  
@PaoloBergantino You, sir, are a gentleman and a scholar. –  TigOldBitties May 19 '12 at 15:43
18  
Wow. I was horrified at first by the solution Paolo proposed, but that took a back seat to the horror I felt upon reading the first comment: "That's very pythonic. Good job!" I'm so disturbed that such a bright community thinks using such cryptic methods for something so basic is a good idea. Why isn't it just s.reverse()? –  odigity Feb 4 '13 at 19:49
14  
@odigity: Perhaps until you understand Python you should reserve your judgment. –  Paolo Bergantino Feb 4 '13 at 20:37
show 12 more comments
up vote 78 down vote

@Paolo's s[::-1] is fastest; a slower approach (maybe more readable, but that's debatable) approach is ''.join(reversed(s)).

share|improve this answer
47  
A lot faster: $ python -m timeit s='s = "abcdef"' 'mystr = mystr[::-1]' 1000000 loops, best of 3: 0.263 usec per loop $ python -m timeit s='s = "abcdef"' 'mystr = "".join(reversed(mystr))' 100000 loops, best of 3: 2.29 usec per loop –  telliott99 Jan 23 '10 at 17:55
 
Looks like about an order of magnitude faster. –  Bepetersn Sep 22 '13 at 2:00
 
@telliott99, there's a syntax error at s='s = ? –  smci Nov 13 '13 at 19:41
1  
I prefer the "reversed()" solution. Readability counts. –  guettli Dec 6 '13 at 13:21
add comment

protected by Jon Clements Apr 11 '13 at 8:29

This question is protected to prevent "thanks!", "me too!", or spam answers by new users. To answer it, you must have earned at least 10 reputation on this site.

Not the answer you're looking for? Browse other questions tagged or ask your own question.