Best way to ensure that an operation is not performed on the same value in a dictionary twice?

Question

Currently I am doing it like this..

def operation(x):
    return x

items_seen = []
d = {"a":10, "b": 5,"c": 6,"d": 7, "e": 7}

for x in d.values():

    if x not in items_seen:
        print operation(x)
        items_seen.append(x)

But I was wondering if there was a better way.. ?

Answer 1

You can convert your values list to a set first to ensure that every value only occurs once:

for x in set(aList.values()):
    print operation(x)

Answer 2

If you only want to apply the operation function to the unique values of a dictionary, you can iterate over the set of its values:

def operation(x):
    return x

d = {"a": 10, "b": 5, "c": 6, "d": 7, "e": 7}

for x in set(d.values()):
    print operation(x)

Output

10
5
6
7

Aside: I've changed your dictionary name from aList to d for clarity.