mylist[ mylist[ mylist [ mystring "hello worldmystring[ 'lmystring[ 'ztraceback (most recent call last)file ""line in typeerror'strobject does not support item assignment the first line creates list of four numbers indexing position returns the value (as usualindexes start at the next command assigns the value to the item in position after the assignmentevaluating the list shows that the new value has replaced the old attempting similar operation on string produces an error strings are not mutablelists are string representation and message encoding string representation hopefullyyou are starting to get the hang of computing with textual (stringdata howeverwe haven' yet discussed how computers actually manipulate strings in you saw that numbers are stored in binary notation (sequences of zeros and ones)the computer cpu contains circuitry to do arithmetic with these representations textual information is represented in exactly the same way underneathwhen the computer is manipulating textit is really no different from number crunching to understand thisyou might think in terms of messages and secret codes consider the age-old grade school dilemma you are sitting in class and want to pass note to friend across the room unfortunatelythe note must pass through the handsand in front of the curious eyesof many classmates before it reaches its final destination andof coursethere is always the risk that the note could fall into enemy hands (the teacher'sso you and your friend need to design scheme for encoding the contents of your message one approach is to simply turn the message into sequence of numbers you could choose number to correspond to each letter of the alphabet and use the numbers in place of letters without too much imaginationyou might use the numbers - to represent the letters - instead of the word "sourpuss,you would write " to those who don' know the codethis looks like meaningless string of numbers for you and your friendhoweverit represents word this is how computer represents strings each character is translated into numberand the entire string is stored as sequence of (binarynumbers in computer memory it doesn' really matter what number is used to represent any given character as long as the computer is consistent