[Tutor] Changing the value in a list

[Ken G.]

If the following program change list[2] to 2010, replacing 1997 (and it 
does), why doesn't the second program work in changing line[ 9:11] to 20 
from 08? 

FIRST PROGRAM:

    list = ['physics', 'chemistry', 1997, 2000]
    print list[2]
    list[2] = 2010
    print list[2]

OUTPUT:

    1997
    2010

SECOND PROGRAM:
    line = [2010020820841134]
    if line[ 9:11] == "08":
        line[ 9:11] = 20
        print line[ 9:11]

OUTPUT:

    "TypeError: 'str' object does not support item assignment."


Thanking you all in advance,

Ken