Getting first n unique elements from Python list

Question

I have a python list where elements can repeat.

>>> a = [1,2,2,3,3,4,5,6]

I want to get the first n unique elements from

Answer 1

You can use OrderedDict or, since Python 3.7, an ordinary dict, since they are implemented to preserve the insertion order. Note that this won't work with sets.

N = 3
a = [1, 2, 2, 3, 3, 3, 4]
d = {x: True for x in a}
list(d.keys())[:N]