Concatenation of many lists in Python [duplicate]

Answer 1

I like itertools.chain approach because it runs in linear time (sum(...) runs in qudratic time) but @Jochen didn't show how to deal with lists of dynamic length. Here is solution for OP's question.

import itertools
list(itertools.chain(*[getNeighbors(n) for n in getNeighbors(vertex)]))

You can get rid of list(...) call if iterable is sufficient for you.