python - Finding elements not in a list

Question

So heres my code:

item = [0,1,2,3,4,5,6,7,8,9]
z = []  # list of integers

for item in z:
    if item not in z:
        print item

z contains a list of integers. I want to compare item to z and print out the numbers that are not in z when compared to item.

I can print the elements that are in z when compared not item, but when I try and do the opposite using the code above nothing prints.

Any help?

Answer 1

Your code is not doing what I think you think it is doing. The line for item in z: will iterate through z, each time making item equal to one single element of z. The original item list is therefore overwritten before you've done anything with it.

I think you want something like this:

item = [0,1,2,3,4,5,6,7,8,9]

for element in item:
    if element not in z:
        print(element)

But you could easily do this like:

[x for x in item if x not in z]

or (if you don't mind losing duplicates of non-unique elements):

set(item) - set(z)