Replacing same substring occurrences of a string with different substrings from looping in python

Question

I am new to python and I want to replace same substring occurrences of a particular string with different substrings by using python. I already tried the .replace() function of python, but it replaces all the occurrences with the new substring. Example for the question is below.

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string = "I am a student as well as a teacher" Here I want to replace the substring "as" with "xas" and "yas" by adding extra character to the substring. The final result should be "I am a student xas well yas a teacher"

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Code that I have tried:

string = "I am a student as well as a teacher"
 occurrences = re.findall("as", string)
 substr = ["xas","yas"]
 i = 0
 for occur in occurrences:
     string = string.replace(occur, substr[i])
     i = i + 1`

Answer 1

You can use regex as well:

substr = ["xxx","yyy"]

def replace_with(_):
    """Returns first value of substr and removes it."""
    return substr.pop(0)

import re

string = "I am a student as well as a teacher"

print(re.sub("as",replace_with,string)) 

Output:

I am a student xxx well yyy a teacher

But the solution using str.replace() with a limit of 1 by Daweo is more elegant.

Answer 2

You can inform replace how many times it should replace following way

s = "I am a student as well as a teacher"
s = s.replace("as","xxx",1)
print(s) #I am a student xxx well as a teacher
s = s.replace("as","yyy",1)
print(s) #I am a student xxx well yyy a teacher

EDIT: Replacing first as with xas and second as with yas requires different approach

s = "I am a student as well as a teacher"
repl = ["xas","yas"]
s = s.split("as")
for i in repl:
    s = [i.join(s[:2])]+s[2:]
s = s[0]
print(s) #I am a student xas well yas a teacher

Note that this solution assumes number of elements of repl is exatcly equal to number of as in s.