How to insert in a string @ a index

[a.m.]

Thanks guys for you help. I ended up doing this way (for the
records)...

t1 = "hello world hello. hello. \nwhy world hello"

while index<t1.count("hello"):

if (your condition to determine keyword):
t2=t1[:(index+offset)].replace("hello","XYZhello")+t1[((index
+offset):] # offset is 5 (hello = 5 characters)

index+=1