How can I compare two lists in python and return matches

Question

I want to take two lists and find the values that appear in both.

a = [1, 2, 3, 4, 5] b = [9, 8, 7, 6, 5]  returnMatches(a, b) 

would return [5], for instance.

Answer 1

Not the most efficient one, but by far the most obvious way to do it is:

>>> a = [1, 2, 3, 4, 5] >>> b = [9, 8, 7, 6, 5] >>> set(a) & set(b) {5} 

if order is significant you can do it with list comprehensions like this:

>>> [i for i, j in zip(a, b) if i == j] [5] 

(only works for equal-sized lists, which order-significance implies).