compare 2 list of lists partially

I have 2 list of lists:

a = [[1, 2, 3], [1, 2, 8], [1, 3, 3]]
b = [[1, 2, 5], [1, 2, 9], [5, 3, 3]]

I want to only get the lists from b that have the same 2 first elements with lists in a
from my example return [1, 2, 5] and [1, 2, 9]

Create a list of tuples consisting of the first two values of each list in a, then use that to filter the entries in b:

allowed_prefixes = [(v[0], v[1]) for v in a]
filtered_b = [v for v in b if (v[0], v[1]) in allowed_prefixes]

As Jorge Luis notes in the comments, using the prefix list to create a set will give the in operator a performance boost:

allowed_prefixes = {(v[0], v[1]) for v in a}

You can by using a list comprehension :

a = [[1, 2, 3], [1, 2, 8], [1, 3, 3]]
b = [[1, 2, 5], [1, 2, 9], [5, 3, 3]]

result = [list_b for list_b in b if list_b[:2] in [list_a[:2] for list_a in a]]

If you want a match of sublists at the same positions:

matches = [lb for la,lb in zip(a,b) if la[:2]==lb[:2]]

if you want matches with any list in a regardless of positions:

prefixes = { tuple(la[:2]) for la in a }
matches  = [lb for lb in b if tuple(lb[:2]) in prefixes]