Python - Replacing Nth occurrence of multiple characters in a String with the given character

Replacing the Nth occurrence of multiple characters in a string with a given character involves identifying and counting specific character occurrences.

Using a Loop and find()

Using a loop and find() method allows us to search for the first occurrence of a substring within each list element. This approach is useful when you need to identify and process specific patterns or characters within the list elements.

s = "hello world, hello everyone"
chars = ['h', 'e']
n = 2
replacement = 'X'

result = s
for char in chars:
    count = 0
    i = -1
    while count < n:
        i = result.find(char, i + 1)
        if i == -1:
            break
        count += 1
    if i != -1:
        result = result[:i] + replacement + result[i + 1:]

print(result)  # Output: "hello world, Xllo everyone"

hello world, XXllo everyone

Explanation:

• The code iterates over each character in chars and uses find() to locate the N-th occurrence of that character in the string.
• Upon finding the N-th occurrence, it replaces the character with X and updates the string; if the N-th occurrence is not found, it leaves the string unchanged.

Using enumerate and String Slicing

Using enumerate() with string slicing allows efficient iteration through a string while keeping track of the index. This technique is useful for modifying specific characters based on their position in the string.

s = "banana island eagle"
targets = {'a', 'e', 'i'}
n = 2
replacement = '*'

count = {char: 0 for char in targets}
for i, char in enumerate(s):
    if char in targets:
        count[char] += 1
        if count[char] == n:
            output = s[:i] + replacement + s[i+1:]
            break
else:
    output = s

print(output)

ban*na island eagle

Explanation:

• The code tracks occurrences of target characters (a, e, i) in the string.
• Upon finding the N-th occurrence, it replaces that character with * and exits the loop.