Python String doesn’t have a built-in reverse() function. However, there are various ways to reverse a string in Python.
Some of the common ways to reverse a string are:
reverse()
functiondef reverse_slicing(s):
return s[::-1]
input_str = 'ABç∂EF'
if __name__ == "__main__":
print('Reverse String using slicing =', reverse_slicing(input_str))
If you run above Python script, the output will be:
Reverse String using slicing = FE∂çBA
def reverse_for_loop(s):
s1 = ''
for c in s:
s1 = c + s1 # appending chars in reverse order
return s1
input_str = 'ABç∂EF'
if __name__ == "__main__":
print('Reverse String using for loop =', reverse_for_loop(input_str))
Output: Reverse String using for loop = FE∂çBA
def reverse_while_loop(s):
s1 = ''
length = len(s) - 1
while length >= 0:
s1 = s1 + s[length]
length = length - 1
return s1
input_str = 'ABç∂EF'
if __name__ == "__main__":
print('Reverse String using while loop =', reverse_while_loop(input_str))
def reverse_join_reversed_iter(s):
s1 = ''.join(reversed(s))
return s1
def reverse_list(s):
temp_list = list(s)
temp_list.reverse()
return ''.join(temp_list)
def reverse_recursion(s):
if len(s) == 0:
return s
else:
return reverse_recursion(s[1:]) + s[0]
We can reverse a string through multiple algorithms. We have already seen six of them. But which of them you should choose to reverse a string. We can use timeit module to run multiple iterations of these functions and get the average time required to run them. All the above functions are stored in a python script named string_reverse.py
. I executed all these functions one by one for 1,00,000 times using the timeit module and got the average of the best 5 runs.
$ python3.7 -m timeit --number 100000 --unit usec 'import string_reverse' 'string_reverse.reverse_slicing("ABç∂EF"*10)'
100000 loops, best of 5: 0.449 usec per loop
$ python3.7 -m timeit --number 100000 --unit usec 'import string_reverse' 'string_reverse.reverse_list("ABç∂EF"*10)'
100000 loops, best of 5: 2.46 usec per loop
$ python3.7 -m timeit --number 100000 --unit usec 'import string_reverse' 'string_reverse.reverse_join_reversed_iter("ABç∂EF"*10)'
100000 loops, best of 5: 2.49 usec per loop
$ python3.7 -m timeit --number 100000 --unit usec 'import string_reverse' 'string_reverse.reverse_for_loop("ABç∂EF"*10)'
100000 loops, best of 5: 5.5 usec per loop
$ python3.7 -m timeit --number 100000 --unit usec 'import string_reverse' 'string_reverse.reverse_while_loop("ABç∂EF"*10)'
100000 loops, best of 5: 9.4 usec per loop
$ python3.7 -m timeit --number 100000 --unit usec 'import string_reverse' 'string_reverse.reverse_recursion("ABç∂EF"*10)'
100000 loops, best of 5: 24.3 usec per loop
The below table presents the results and slowness of an algorithm from the best one.
Algorithm | TimeIt Execution Time (Best of 5) | Slowness |
---|---|---|
Slicing | 0.449 usec | 1x |
List reverse() | 2.46 usec | 5.48x |
reversed() + join() | 2.49 usec | 5.55x |
for loop | 5.5 usec | 12.25x |
while loop | 9.4 usec | 20.94x |
Recursion | 24.3 usec | 54.12x |
We should use slicing to reverse a string in Python. Its code is very simple and small and we don’t need to write our own logic to reverse the string. Also, it’s the fastest way to reverse a string as identified by the above test executions.
You can checkout complete python script and more Python examples from our GitHub Repository.
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Hi, Thank you for the explanation. I also wanted to know how to add new lines to the output. For example I have made a reverse string input program: def reverse_slice(s): return s[::-1] s=input('enter a string ') print(s[::-1]) How would I a make my answer be on multiple lines?
- J
Hi, Could you please help to explain the logic, as in what does Python do, for 1.1) Python Reverse String using Slicing. Confusing part are the double colon operators. I understand the first one is to tell Python to look at all the elements in string, the second one I’m unsure about but [ -1] means that the first item to return needs to be at length [-1]. What does the second colon operator tell Python to do? Thanks
- Kai
great content thanks
- anonymus
Hi Pankaj, very useful indeed. I have a question: Why is this piece of code picking the character in the last position of the string and not the char in the position zero of the string? (if I move the char operand in the assignment statement to the other side of the operator then Python picks the char in position zero) s1 = c + s1 # appending chars in reverse order Thanks for clarifying. Rody
- Rody
thanks for uploading very useful
- spandana