How can i delete duplicate letter, but adding some exception letter to it

im trying to do data cleaning from instagram using python.
i need to remove those duplicate letters, but on (a,g) only remove them until there are 2 duplicate letters (aa,gg)

so it looks like this
input : mengganti, maaf, ppuuutttiiiihhh, mmmmeeeeerrrraaaah, maaagggz
output desired : mengganti, maaf, putih, meraah, maaggz

what im currently doing with regex is like this:

re.compile(r'(.)\1{1,}', re.IGNORECASE).sub(r'\1',kalimat)

input : mengganti, maaf, ppuuutttiiiihhh, mmmmeeeeerrrraaaah, maaagggz
currrent output : menganti, maf, putih, merah,magz
NB: it doesnt have to use regex

Solution

You can first capture a and g and replace with 2 times group 1.

([ag])\1+

The pattern matches:

([ag]) Capture group 1, match either a or g
\1+ Repeat 1+ times the same char matched in group 1

Then replace all chars other than a g or a whitespace char, and replace with a single group 1 to remove the duplicates.

([^\sag])\1+

The pattern matches:

( Capture group 1
- [^\sag] Match a non whitespace char except for a or g
) Close group 1
\1+ Repeat 1+ times the same char matched in group 1

For example

import re

s = "mengganti, maaf, ppuuutttiiiihhh, mmmmeeeeerrrraaaah, maaagggz"

print(re.sub(
        r"([^\sag])\1+",
        r"\1",
        re.sub(r"([ag])\1+", r"\1\1", s))
)

Output

mengganti, maaf, putih, meraah, maaggz

See a Python demo.

Or using a single pattern with an alternation | combining the 2 patterns having 2 capture groups, and using re.sub with a lambda:

import re

pattern = r"([ag])\1+|([^\sag])\2+"
s = "mengganti, maaf, ppuuutttiiiihhh, mmmmeeeeerrrraaaah, maaagggz"
result = re.sub(
        pattern,
        lambda x: x.group(1) * 2 if x.group(1) else x.group(2),
        s
)

if result:
        print(result)

Output

mengganti, maaf, putih, meraah, maaggz

See another Python demo or a regex demo