Reverse a String
Reverse a string in Python.
String reversal is a fundamental operation in programming that helps you understand string manipulation, slicing syntax, and iteration patterns. In this exercise, you will implement a function that reverses a string without using the built-in slicing shortcut.
š Concepts & Theory
In Python, strings are immutable sequences of characters, which means you cannot modify them in place. To reverse a string, you have several approaches:
Method 1: String Slicing (Most Pythonic)
Python's slicing syntax allows you to reverse a string with [::-1]. The syntax [start:stop:step] with a step of -1 means "go backwards from end to start".
text = "hello"
reversed_text = text[::-1] # "olleh"Method 2: Manual Loop (Educational)
For learning purposes, you can manually build the reversed string by prepending each character:
text = "hello"
result = ""
for char in text:
result = char + resultMethod 3: Using reversed() Function
The built-in reversed() function returns an iterator that you can join:
text = "hello"
reversed_text = "".join(reversed(text))Each method has its use case: slicing is fastest, manual loop is educational, and reversed() is memory-efficient for large strings.
šÆ Your Challenge
Write reverse_string without [::-1].
š Starter Code
def reverse_string(text):
pass
print(reverse_string('hello'))- Think about building a new string from right to left
- Each character should be added to the front of your result
- The prepend operation is: new_char + existing_string
Solution
def reverse_string(text):
result = ''
for char in text:
result = char + result
return result
print(reverse_string('hello'))Explanation
This solution uses a manual approach by iterating through each character and prepending it to the result string. By placing each character at the beginning (char + result instead of result + char), we effectively reverse the order. While not the most efficient method due to string immutability creating new objects, it clearly demonstrates the reversal logic. Time complexity: O(nĀ²) due to string concatenation. The slicing method [::-1] would be O(n) and more Pythonic.
ā ļø Common Mistakes to Avoid
- Forgetting that strings are immutable in Python
- Using result + char instead of char + result (doesn't reverse)
- Not returning the result from the function
- Trying to modify the string in-place like result[i] = char