To reverse a string in Python, here are the most common and efficient methods:
1. Using Slicing (Most Pythonic)
s = "hello"
reversed_str = s[::-1] # "olleh"Explanation:
- The slice
[::-1]reverses the string by stepping backward with a step size of-1.
2. Using reversed() + join()
s = "world"
reversed_str = ''.join(reversed(s)) # "dlrow"Explanation:
reversed(s)returns an iterator over the characters in reverse order.''.join()combines these characters into a new string.
3. Using a Loop
s = "python"
reversed_str = ""
for char in s:
reversed_str = char + reversed_str # Prepends each character
# Result: "nohtyp"Optimized version (using a list for efficiency):
reversed_str = []
for char in reversed(s):
reversed_str.append(char)
reversed_str = ''.join(reversed_str)4. Using a List and reverse()
s = "example"
char_list = list(s)
char_list.reverse()
reversed_str = ''.join(char_list) # "elpmaxe"Key Notes
- Immutability: All methods create a new string (original string remains unchanged).
- Edge Cases:
- Empty string: Returns empty.
- Unicode characters: Handled correctly (e.g.,
"🚀🌎"→"🌎🚀"). - Efficiency: Slicing (
[::-1]) is fastest and most concise.
Performance Comparison
| Method | Time Complexity | Use Case |
|---|---|---|
Slicing ([::-1]) | O(n) | Best for most cases |
reversed() + join | O(n) | Readable alternative |
| Loop | O(n) | Pedagogical/iterative logic |
List reverse() | O(n) | Intermediate list operations |
Example with Input/Output
original = "Hello, World!"
reversed_str = original[::-1]
print(reversed_str) # "!dlroW ,olleH"When to Use Which?
- Slicing: Default choice for simplicity and speed.
reversed(): Useful in functional programming contexts.- Loops: For teaching/learning or custom reversal logic.
- List
reverse(): Rarely needed, but works if already using list operations.
All methods handle standard ASCII and Unicode strings correctly. For advanced scenarios (e.g., grapheme clusters), use libraries like unicodedata.