Comparing two lists and only printing the differences? (XORing two lists)

Question

I\'m trying to create a function that takes in 2 lists and returns the list that only has the differences of the two lists.

Example:

a = [1,2,5,7,9]         


        

Answer 1

Use set is better

>>> a = [1,2,5,7,9]
>>> b = [1,2,4,8,9]
>>> set(a).symmetric_difference(b)
{4, 5, 7, 8}

Thanks to @DSM, a better sentence is:

>>> set(a)^set(b)

These two statements are the same. But the latter is clearer.

Update: sorry, I did not see the last requirement: cannot use set. As far as I see, the solution provided by @sashkello is the best.