Python String doesn’t have a built-in reverse() function. However, there are various ways to reverse a string in Python.
1. How to Reverse a String in Python?
Some of the common ways to reverse a string are:
- Using Slicing to create a reverse copy of the string.
- Using for loop and appending characters in reverse order
- Using while loop to iterate string characters in reverse order and append them
- Using string join() function with reversed() iterator
- Creating a list from the string and then calling its reverse() function
- Using Recursion
1.1) Python Reverse String using Slicing
def 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∂çBA1.2) Reverse String using For Loop
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
1.3) Reverse a String using While Loop
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))1.4) Reverse a String using join() and reversed()
def reverse_join_reversed_iter(s): s1 = ''.join(reversed(s)) return s11.5) Python Reverse String using List reverse()
def reverse_list(s): temp_list = list(s) temp_list.reverse() return ''.join(temp_list)1.6) Python Reverse String using Recursion
def reverse_recursion(s): if len(s) == 0: return s else: return reverse_recursion(s[1:]) + s[0]2. Best Way to Reverse a String in Python
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
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 |
3. Summary
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.
4. References
- reversed() API Doc
- str.join() API Doc