You're thinking of a finite map, also called a hash table or a dictionary.

The map function takes a function and a list and applies the function to every element of the list:

  map(double,[1,2,3]) = [2,4,6]

Grandparent could've used the for loop rather than the map function to make his point:

  for i in [1,2,3]:
      print i * 2

-- because in general instead of the i * 2 we might have a call to a function that might raise an exception.

ADDED. That is wrong: the for loop would not a good example at all because it is not customary to declare the type of a for loop or to need to declare which exceptions a `for` loop might throw.