How to efficiently remove the same-length elements from a list in python

Question

For example, I have a list:

[[1,3],[23,4],[13,45,6],[8,3],[44,33,12]]

Is there any efficient way that I can finally get the list below?

[[1,3],[13,45,6]]

For every length of the list, keep only one element.

Answer 1

Just make a dictionary keyed off the length and get its values:

>>> l = [[1,3],[23,4],[13,45,6],[8,3],[44,33,12]]
>>> dict((len(i), i) for i in l).values()
[[8, 3], [44, 33, 12]]

Answer 2

s = set() [e for e in l if len(e) not in s and s.add(len(e)) is None]