It is tempting to use the  operator on the left side of an assignment, with the intention of changing a character in a string. For example:
>>> greeting = 'Hello, world!'>>> greeting = 'J'TypeError: 'str' object does not support item assignment
The “object” in this case is the string and the “item” is the character you tried to assign. For now, an object is the same thing as a value, but we will reﬁne that deﬁnition later. An item is one of the values in a sequence.
The reason for the error is that strings are immutable, which means you can’t change an existing string. The best you can do is create a new string that is a variation on the original:
>>> greeting = 'Hello, world!'>>> new_greeting = 'J' + greeting[1:]>>> print new_greetingJello, world!
This example concatenates a new ﬁrst letter onto a slice of greeting. It has no effect on the original string.