Vfrdtyky

I want to write a program that shows all the possible ways a combination of different coins (5c, 10c, 50c, etc.) can amount to a certain value (for instance, $4). Let's say, for starters, I only want to consider 50c, $1 and 2$ into the possible combinations. If I want to use brute force, I could write 3 nested while loops and return that combination of currency every time they sum up to the value I want (in this case, $4). However, as we consider more currency options (for instance, 1c, 5c, 10c, 25c, 50c, $1, $2, $5, $10, $50, $100) and bigger sums (let's say I want all combinations to get $400), the code becomes very verbose and difficult to mantain. If I want to make a generic algorithm that works for any country and combination of currencies, I can't rely on simple loop nesting.

Given this problem, I've tried using decorators so I can nest the loops in a single function:

INTENDED_SUM = 400



coin_count = {

    200: 0,

    100: 0,

    50: 0,

}



def max_range(value):

    return INTENDED_SUM / value



def coin_loop(coin_value):

    def decorator(func):

        while coin_count[coin_value] <= max_range(coin_value):

            yield from func()

            coin_count[coin_value] += 1

        else:

            coin_count[coin_value] = 0

    return decorator





@coin_loop(100)

def get_combinations():

    agg = sum([i * coin_count[i] for i in coin_count])

    if agg == INTENDED_SUM:

        yield coin_count



for i in get_combinations:

    print(i)

This is the output:

{200: 0, 100: 4, 50: 0}

However, if I add multiple decorators to the get_combinations() function, a TypeError is raised:

@coin_loop(200)

@coin_loop(100)

@coin_loop(50)

def get_combinations():

    agg = sum([i * coin_count[i] for i in coin_count])

    if agg == INTENDED_SUM:

        yield coin_count



Traceback (most recent call last):

  File "31-coin_sums.py", line 29, in <module>

    for i in get_combinations:

  File "31-coin_sums.py", line 15, in decorator

    yield from func()

TypeError: 'generator' object is not callable

So I have two questions:

1. 
   

   Why does get_combinations already shows up as a generator and does not need to be called when I call it in the last 2 lines of the code? Shouldn't they be like this?

   
   
   

   for i in get_combinations():
   
       print(i)
   
   

   
   


2. 
   

   Why isn't decorator nesting working in this case? Expected output should be something like:

   
   
   

   {200: 2, 100: 0, 50: 0}
   
   {200: 1, 100: 2, 50: 0}
   
   {200: 1, 100: 1, 50: 2}
   
   {200: 1, 100: 0, 50: 4}
   
   {200: 0, 100: 4, 50: 0}
   
   {200: 0, 100: 3, 50: 2}
   
   {200: 0, 100: 2, 50: 4}
   
   {200: 0, 100: 1, 50: 6}
   
   {200: 0, 100: 0, 50: 8}
   
   

   
   

EDIT: just as an example, I want the code above (with multiple decorators) to be equivalent to this, except without nested whiles:

INTENDED_SUM = 400



coin_count = {

    200: 0,

    100: 0,

    50: 0,

}



def max_range(value):

    return INTENDED_SUM / value



def get_combinations():

    while coin_count[200] <= max_range(200):

        while coin_count[100] <= max_range(100):

            while coin_count[50] <= max_range(50):

                agg = sum([i * coin_count[i] for i in coin_count])

                if agg == INTENDED_SUM:

                    yield coin_count

                coin_count[50] += 1

            else:

                coin_count[50] = 0

            coin_count[100] += 1

        else:

            coin_count[100] = 0

        coin_count[200] += 1

    else:

        coin_count[200] = 0



for i in get_combinations():

    print(i)