python - Checking if any elements in one list are in another

Question

I'm trying to compare two lists and simply print a message if any value from the first list is in the second list.

def listCompare():
  list1 = [1, 2, 3, 4, 5]
  list2 = [5, 6, 7, 8, 9]
  if list1 in list2:
    print("Number was found")
  else:
    print("Number not in list")

In this example, I want the if to evaluate to True because 5 is in both lists. This doesn't work, and I'm not sure of the simplest way to compare the two lists.

Answer 1

You could solve this many ways. One that is pretty simple to understand is to just use a loop.

def comp(list1, list2):
    for val in list1:
        if val in list2:
            return True
    return False

A more compact way you can do it is to use map and reduce:

reduce(lambda v1,v2: v1 or v2, map(lambda v: v in list2, list1))

Even better, the reduce can be replaced with any:

any(map(lambda v: v in list2, list1))

You could also use sets:

len(set(list1).intersection(list2)) > 0