Python program to change character of a string using given index

Strings in Python are immutable, meaning you cannot modify individual characters directly. When you need to change a character at a specific index, you must create a new string using slicing and concatenation.

For example, if we have s = "python", i = 3, and c = 'P', attempting s[i] = c will raise a TypeError: 'str' object does not support item assignment.

Algorithm

To replace a character at index i with character c ?

• Extract the left part: s[0:i]

• Extract the right part: s[i+1:]

• Concatenate: left + c + right

Using String Slicing

The most common approach uses Python's slice notation ?

def change_character(s, i, c):
    left = s[:i]
    right = s[i+1:]
    return left + c + right

# Example usage
s = "python"
i = 3
c = 'P'
result = change_character(s, i, c)
print(f"Original: {s}")
print(f"Modified: {result}")

Original: python
Modified: pytPon

Using List Conversion

Convert string to list, modify, then join back ?

def change_character_list(s, i, c):
    char_list = list(s)
    char_list[i] = c
    return ''.join(char_list)

# Example usage
s = "python"
i = 3
c = 'P'
result = change_character_list(s, i, c)
print(f"Original: {s}")
print(f"Modified: {result}")

Original: python
Modified: pytPon

Multiple Character Changes

To change multiple characters at different positions ?

def change_multiple_characters(s, changes):
    char_list = list(s)
    for index, char in changes.items():
        if 0 <= index < len(char_list):
            char_list[index] = char
    return ''.join(char_list)

# Example usage
s = "python"
changes = {1: 'Y', 3: 'P', 5: 'N'}
result = change_multiple_characters(s, changes)
print(f"Original: {s}")
print(f"Modified: {result}")

Original: python
Modified: pYtPoN

Comparison

Conclusion

Use string slicing for single character replacement and list conversion for multiple changes. Both methods create new string objects due to Python's string immutability.