Changing values in list: Python

I'm making a function to modify the elements in a list, but it doesn't change all the way through... My function is:

def modifyValues(l):
    for x in l:
        if x == 1:
            l[x] = 'a'
        elif x == 2:
            l[x] = 'b'
        elif x == 3:
            l[x] = 'c'
    print (l)

when

modifyValues([1, 2, 3, 2, 3, 1, 2, 2])

the output is:

['a', 'b', 'c', 2, 3, 1, 2, 2]

Why doesn't it change every value?

When you iterate through the loop, you are iterating the loop elements and not the indexes. You need to use enumerate to get the indexes along with the values.

A small demo can be

def modifyValues(l):
    for i,x in enumerate(l):   # Use enumerate here. 
        if x == 1:
            l[i] = 'a'
        elif x == 2:
            l[i] = 'b'
        elif x == 3:
            l[i] = 'c'
    print (l)

Output

['a', 'b', 'c', 'b', 'c', 'a', 'b', 'b']