Strings don’t have any methods on them that allow a change to the value of the string. In other words: strings are immutable.
When you call str.replace
a new string is built and returned.
>>> s1 = 'Rohit'
>>> s2 = s1.replace('R', 'M')
>>>
>>> s1
'Rohit'
>>> s2
'Mohit'
As you can see s1
still has its original value.