One line "x = for... if y not in x"

Question

I would like to make the for... if in the following code into one line:

cities = ["Berlin", "Berlin", "Berlin", "London"]

unique_cities = []

for city in cities:
    if city not in unique_cities:
        unique_cities.append(c)

print unique_cities

I imagine something like this:

unique_cities = [city for city in cities if city not in unique_cities]

which of course doesn't work because unique_cities is not defined in that loop.

How would I make a one-liner out of this?

I duped this of the recipe that preserves order; if order doesn't need to be preserved, just use `set()`. — Martijn Pieters, Nov 05 '14 at 13:06
Nominating to re-open, I think Juicy generally asks about how to write a Python construction more briefly, and only gives `unique` as an example problem that could use that. — Kos, Nov 05 '14 at 13:07
@Kos: you cannot generalise writing one-liners, no. And that would be **way** too broad a question if true. — Martijn Pieters, Nov 05 '14 at 13:08
Hm... Okay, I'm convinced (also on the ground that this looks a bit like an XY question). — Kos, Nov 06 '14 at 09:46

score 1 · Answer 1 · answered Nov 05 '14 at 13:05

1

If order is not important, the easier way to accomplish this is just

unique_cities = list(set(cities))

answered Nov 05 '14 at 13:05

Cory Kramer

114,268
16
167
218

score 1 · Answer 2 · answered Nov 05 '14 at 13:05

1

I think it would be easier to turn it into a set:

unique_cities = set(cities)

answered Nov 05 '14 at 13:05

John Szakmeister

44,691
9
89
79

One line "x = for... if y not in x"

2 Answers2