Replace max 2 occurrences of characters with a colon

re.sub(“[ ,.]”, “:”, text, 2)

Replace maximum 2 occurrences of space, comma, or dot with a colon.

import re

S = 'Python Exercises, PHP exercises.'

print(re.sub("[ ,.]", ":", S, 2))

Output:

Python:Exercises: PHP exercises.

See also

https://www.w3resource.com/python-exercises/re/python-re-exercise-32.php