How to Reverse a String in Python Without Using Slicing or Built-in Functions

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Reversing a string is a common task in Python, but what if you want to do it without using slicing or built-in functions like reversed() or join()? In this article, we’ll explore a simple approach to achieve this using a loop.

The typical way to reverse a string in Python is using slicing ([::-1]) or built-in functions (reversed() and join()). However, to reverse a string in Python without using slicing or built-in functions, we need to manually iterate over the string and construct the reversed version.

Using a Loop

We can use a loop to read characters from the end of the string and build the reversed string step by step.

def reverse_string(s):
    reversed_str = ""
    for char in s:
        reversed_str = char + reversed_str  # Prepend each character
    return reversed_str

# Example usage
input_string = "Python"
output_string = reverse_string(input_string)
print("Reversed String:", output_string)
  1. We initialize an empty string reversed_str to store the reversed string.
  2. We iterate through each character in the input string.
  3. Instead of appending the character, we prepend it to reversed_str.
  4. This way, the first character moves to the last position, the second character comes before it, and so on.
  5. Finally, we return the reversed string.

Output:

Reversed String: nohtyP

Alternative Approach: Using a List

Another approach to reverse a string in Python without using slicing or built-in functions is to use a list and construct the reversed string manually.

def reverse_string(s):
    char_list = list(s)  # Convert string to list
    reversed_str = ""
    
    for i in range(len(char_list) - 1, -1, -1):  # Iterate backwards
        reversed_str += char_list[i]
    
    return reversed_str

# Example usage
input_string = "Hello"
output_string = reverse_string(input_string)
print("Reversed String:", output_string)
  • The function first converts the string into a list of characters.
  • It then iterates over the list from the last character to the first.
  • Each character is appended to reversed_str, forming the reversed string.

If you ever need to reverse a string in Python without using slicing or built-in functions, you can rely on simple loops to build the reversed string. Whether by prepending characters or iterating backward, these methods offer a clear and effective way to manually reverse a string.

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