Replace all except the first occurrence of a substring in Python?

Question

I have a string which looks like below

string = "SELECT sdfdsf SELECT sdrrr SELECT 5445ff"

Now I want to replace every occurrence of SELECT except the first one with @@@SELECT so that in the end string looks like this

"SELECT sdfdsf @@@SELECT sdrrr @@@SELECT 5445ff"

Now Python replace() replaces all occurrence of SELECT.

string = string.replace("SELECT", "@@@SELECT)

So the string becomes

"@@@SELECT sdfdsf @@@SELECT sdrrr @@@SELECT 5445ff"

How do I ensure except the first instance, everything else is replaced?

Note: The string can have n occurrences of SELECT

Answer 1

With additional "reversed" substitution step:

s = "SELECT sdfdsf SELECT sdrrr SELECT 5445ff"
res = s.replace("SELECT", "@@@SELECT").replace("@@@SELECT", "SELECT", 1)
print(res)

The output:

SELECT sdfdsf @@@SELECT sdrrr @@@SELECT 5445ff

---

A more sophisticated, but ensuring target word boundaries, could be as below:

import re

def make_replacer():
    rpl = ''
    def inner(m):
        nonlocal rpl
        res = rpl + m.group()
        rpl = '@@@'
        return res
    return inner

s = "SELECT sdfdsf SELECT sdrrr SELECT 5445ff"
res = re.sub(r'\bSELECT\b', make_replacer(), s)
print(res)   # SELECT sdfdsf @@@SELECT sdrrr @@@SELECT 5445ff