Python help num_in_common_between_lists(list1, list2) is a function that calculates the number of common items between two lists. To do this you can have a for loop that iterates over the items of list1 and then an if statement that checks whether or not that item is also in list2. This function is to return an integer, which is the number of items that the two lists had in common (i.e., the number of items that were found in both of the lists). (e.g., if list1 = [1,3,5,6] and list2 = [1, 2, 3], then the value 2 would be returned since they have two items in common (the values 1 and 3)). def num_in_common_between_lists(list1, list2): ''' Remember the docstring''' pass # this is a placeholder that you will replace with Python code