Strings are unmutable, lists are mutable (1)

Strings are unmutable, i.e. you cannot directly change an element:

aString = "Back"
# try to change the "B" to a "J"
aString[0]="J"

prints:

Traceback (most recent call last):
  File "stringmutable.py", line 3, in ?
    aString[0]="J"
TypeError: object doesn't support item assignment