[Python] Efficiently filtering out 'None' items in a list comprehension in which a function is...

I have a list comprehension that calls a function which potentially returns None.

f = lambda x: x if x < 3 else None
l = [f(x) for x in [1,2,3,4]] # [1, 2, None, None]


I'd like to have the list comprehension as above, without the None entries.

What's a more efficient way to do the following, without creating the additional overhead, and while retaining the efficiency of the list comprehension?

filter(None, l) # [1, 2]

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