TypeError: 'int' object is not iterable -- Python map function

Question

I am learning the map function right now. I am creating a function where we can add 2 in all the elements of a list and then print them in a terminal:

def add_twoineach(a):
    for i in a:
        i = i + 2
        print(i)

Till here it is all good.

I am trying to use map function to iterate through a list and add 2 to each of the element of a list:

y = list(map(add_twoineach, (1, 2, 3))) 

but I am getting error:

    for i in a:
TypeError: 'int' object is not iterable

Answer 1

It might help to think in terms of types. Python plays fast and loose with types, so let's have an example in a language that both is strict with its typing and uses map idiomatically -- Haskell.

The only bits of syntax that you might need to know is to read :: as "has type of."

addTwo :: int -> int  -- takes an int and returns an int
addTwo x = x+2
-- this can also be written as addTwo = (+2), but don't worry about that

addTwoMany :: [int] -> [int] -- takes a list of ints and returns a list of ints
addTwoMany xs = map addTwo xs

as you can see, map takes a function that acts on a single value and instead acts on a whole list of values. This concept generalizes beyond lists to a group in Category Theory called "functors," where you take a function that acts on a single value and make it act on a group of those values instead.

Answer 2

When using map, you do not need the for loop anymore as the map applies the function on your iteration

def add_twoineach(a):
    i = a + 2
    return i

y = list(map(add_twoineach, (1, 2, 3)))