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

RomanPerekhrest · Accepted Answer · 2019-10-12 11:46:20Z

10

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

edited Oct 12, 2019 at 11:46

answered Oct 12, 2019 at 11:24

RomanPerekhrest

93.1k4 gold badges75 silver badges112 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Ajax1234 · Accepted Answer · 2019-10-12 15:22:26Z

4

You can use itertools.count with re.sub:

import re, itertools
c = itertools.count()
string = "SELECT sdfdsf SELECT sdrrr SELECT 5445ff"
r = re.sub(r"\bSELECT\b", lambda x:x.group() if not next(c) else f'@@@{x.group()}', string)

Output:

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

However, if SELECT is always placed at the start of the string, you can use a negative lookbehind:

r = re.sub('(?<!^)SELECT', lambda x:f'@@@{x.group()}', string)

Output:

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

answered Oct 12, 2019 at 15:22

Ajax1234

71.7k9 gold badges67 silver badges110 bronze badges

Comments

codrelphi · Accepted Answer · 2019-10-12 11:36:26Z

3

You can use the method partition and replace. The working code looks like:

string = "SELECT sdfdsf SELECT sdrrr SELECT 5445ff"
parts = string.partition("SELECT")  # returns a tuple
results = parts[0] + parts[1] + parts[2].replace("SELECT", "@@@SELECT")

print(results)

So you will get:

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

If string = "Blabla is SELECT sdfdsf SELECT sdrrr SELECT 5445ff", you will get:

Blabla is SELECT sdfdsf @@@SELECT sdrrr @@@SELECT 5445ff

answered Oct 12, 2019 at 11:36

codrelphi

1,0651 gold badge7 silver badges15 bronze badges

Comments

kabanus · Accepted Answer · 2019-10-12 11:45:11Z

3

How about just skipping the first 3 letters of what you have?

string = string.replace("SELECT", "@@@SELECT)[3:]

answered Oct 12, 2019 at 11:45

kabanus

26.3k7 gold badges48 silver badges79 bronze badges

Comments

unknown.prince · Accepted Answer · 2019-10-12 11:32:30Z

1

import string

def removeExceptFirst(s, old, new):
    i = s.find(old) + len(old)
    newStr = s[0:i]
    newStr += s[i:].replace(old, new)
    return newStr

print(removeExceptFirst("SELECT sdfdsf SELECT sdrrr SELECT 5445ff", "SELECT", "@@@SELECT"))

The Output:

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

answered Oct 12, 2019 at 11:32

unknown.prince

7527 silver badges22 bronze badges

Comments

Andrei Odegov · Accepted Answer · 2019-10-13 07:40:13Z

1

One more approach:

import re
from itertools import chain, repeat
string = 'SELECT sdfdsf SELECT sdrrr SELECT 5445ff'
string = ''.join(x + s for x, s in zip(chain(['', 'S'], repeat('@@@S')), re.split(r'\bS(?=ELECT\b)', string)))
print(string)

Output:

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

edited Oct 13, 2019 at 7:40

answered Oct 12, 2019 at 12:02

Andrei Odegov

3,5722 gold badges18 silver badges26 bronze badges

Comments

user12066865 · Accepted Answer · 2019-10-12 11:44:18Z

0

use this code (more simple and only use split and replace)

string = "SELECT sdfdsf SELECT sdrrr SELECT 5445ff"
string = "SELECT " + string.split('SELECT', 1)[1].strip().replace('SELECT', '@@@SELECT').strip()

But if there's a text before the SELECT, use

string = "SELECT sdfdsf SELECT sdrrr SELECT 5445ff"
string = string.split('SELECT', 1)[0].strip() + " SELECT " + string.split('SELECT', 1)[1].strip().replace('SELECT', '@@@SELECT').strip()

That code remove the first SELECT and then replace all the SELECT sub-string and then add the SELECT string to the main string

answered Oct 12, 2019 at 11:44

user12066865

Collectives™ on Stack Overflow

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

7 Answers 7

Comments

Comments

Comments

Comments

Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

7 Answers 7

Comments

Comments

Comments

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related