python function exact change won't work

Question

My assignment is:

where the input target_amount is a single non-negative integer value and the input L is a list of positive integer values. Then, exact_change should return either True or False: it should return True if it's possible to create target_amount by adding up some-or-all of the values in L. It should return False if it's not possible to create target_amount by adding up some-or-all of the values in L.

For example, L could represent the coins you have in your pocket and target_amount could represent the price of an item – in this case, exact_change would tell you whether or not you can pay for the item exactly.

Here are a few examples of exact_change in action. Notice that you can always make change for the target value of 0, and you can never make change for a negative target value: these are two, but not all, of the base cases!

The function I wrote is:

def exact_change( target_amount, L ):
    if target_amount > sum(L):
        return False
    elif target_amount == 0:
        return True
    elif target_amount < 0:
        return False
    elif target_amount > 0 and L==[]:
        return False
    elif target_amount == L:
        return True
    else:
        loseit = exact_change(target_amount, L[1:])
        useit = exact_change(target_amount, L[0])
        return loseit or useit'

And the outcame has to be:

>>> exact_change( 42, [25, 1, 25, 10, 5, 1] )
True
>>> exact_change( 42, [25, 1, 25, 10, 5] )
False
>>> exact_change( 42, [23, 1, 23, 100] )
False
>>> exact_change( 42, [23, 17, 2, 100] )
True
>>> exact_change( 42, [25, 16, 2, 15] )
True  # needs to be able to "skip" the 16...
>>> exact_change( 0, [4, 5, 6] )
True
>>> exact_change( -47, [4, 5, 6] )
False
>>> exact_change( 0, [] )
True
>>> exact_change( 42, [] )
False

But my outcome is:

TypeError: 'int' object is not iterable

Please help me! What am I missing?

Answer 1

For the useit recursive call, you are passing a single int instead of the remaining list, see below:

def exact_change( target_amount, L ):
    if target_amount > sum(L):
        return False
    elif target_amount == 0:
        return True
    elif target_amount < 0:
        return False
    elif target_amount > 0 and not L:
        return False
    else:
        loseit = exact_change(target_amount, L[1:])
        # reduce target amount since we use current coin
        useit = exact_change(target_amount - L[0], L[1:])
        return loseit or useit

Answer 2

You are trying to iterate through a single integer. This is not possible. You iterate through a list.