reverse a string in Python

How to reverse a string?

s = 'abc'
s = s[::-1]
print s


Simple! :-)

Comments

Hans Nowak said…
Yeah, but it might be useful to explain to newbies what the slice notation does. If I were new to Python, then "s[::-1]" would look positively odd to me... I certainly would not think it reverses the string. Just a thought. :-)

--Hans
Tamim Shahriar said…
Thanks for your comment. I didn't explain it as I thought it would be fun for anyone who tries to think how s[::-1] works :)
priyeshsolanki said…
i appreciate.
it really helpful.
thanks.
Teci Pulido said…
Simple yet so useful! Thanks :)
bravo said…
explain how it works ?

or any link for explanation will be helpful.

thanks.
Bhavin Patel: "::" is known as stride notation.

Example:
>>> foo = [2, 5, 1, 8]

Regular slice (returns all)
>>> foo[:]
[2, 5, 1, 8]

Slice with stride (returns every nth)
>>> foo[::2]
[2, 1]

Stride works inversely as well
>>> foo[::-2]
[8, 5]

Hence it can be used to reverse a string (stride backwards using step length of one)
>>> 'foobar'[::-1]
'raboof'

There is another way to reverse as well. This can be done using "reversed" generator:
>>> ''.join([char for char in reversed('foobar')])
'raboof'

As the list comprehension returns a list I had to join it separately. Normally the [::-1] trick should work just fine. "reversed" may be useful in some special cases, however.

Check out http://www.python.org/doc/2.3.5/whatsnew/section-slices.html for more comprehensive documentation.
Praveen Kumar said…
Thank you very much its simple and nice
saikat_rt said…
s = 'abc'

s = s[::2]

print s


#for this code it returns ac
#how
burk said…
it should be "ca", isn't it?
Unknown said…
thanks it is very helpful and explained very well

Does anyone know what i should use to extract string/substring from a string?
praveen said…
That really proves the power of python, for which it would take couple of lines in other languages.
Unknown said…
Python is really a nice language. Just for comparison, that is how i would do it in perl:

print $string = reverse("ABC")
Unknown said…
thanks......workz perfectly as i expected
Anonymous said…
>>>s='spam'
>>>print s[:]
spam
>>>print s[::-1]
maps
>>>print s[0:len(s)]
spam
>>>print s[0:len(s):-1]
(prints nothing)

Any reason, why ??
redDevil said…
@saikat

s='abc'
print s[::-2]

returns 'ca' only...
casper said…
i'm new to python, i need a program to convert any decimal number in to octal(base 8):using python 2.7 ,can any one give me an idea how to write it :please help me~!
Nat said…
@casper

You could do this:
oct(12)

that would return
'014' as a string

To enter an octal number literal, precede with a 0:
0122 will return 82 in base 10

to go from an octal string to an int:
int('014',8)
Nat said…
This comment has been removed by the author.
a said…
This comment has been removed by the author.
a said…
You can also use this technique to reverse words in a sentence:

>>> sentence = "one two three four"
>>> ' '.join( [ word[::-1] for word in sentence.split() ] )[::-1]
'four three two one'
J.Naveen said…
The above example is simplified as

>>> sentence = "one two three four"
>>> ' '.join( [ word for word in sentence.split() ] [::-1])
'four three two one'
Smileman said…
but when I tried it, it doesn't print the space between the reversed i.e the output is like this fourthreetwoone
the_derp said…
Hmm, i did it but here's what I thought regarding this.
[::-1]

[:] <-- this gets all of the string

while [::(value)] skips or reverse the string. if it is negative, the skipping starts from the last character of the string depends on the number.

for example, you can put -2 instead of -1.

s = 'abcdef'
s = s[::-2]
print s

if counted base on the slice number, it would creat a group of three which are fe, dc and ba. the first character of each group (f,d,b) will appended to formed a value and stored it to the variable 's'.
maybe the easiest way is


revword = ''

for letter in reversed(word): revword += letter

print revword
Unknown said…
hey, reverse a string in python
Full code solutions with test data and output, described in clear English and tested on the same page
Unknown said…
str = "hello world"
print (" ".join(str.split()[::-1])) would work for reversing string word by word :)
Thought to share it . :)

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