This page
https://docs.python.org/3/tutorial/introduction.html

states: "Python strings cannot be changed — they are immutable".

As it is written, it is a wrong statement. This example proves it:

>>> myString = 'Python3'
>>> myString 
'Python3'
>>> myString = 'Perl'
>>> myString 
'Perl'
>>> 

Maybe what the documentation intended to say is that we cannot change parts of strings using indexes.