How do I prevent the result print repeatly in Python

Question

It works fine when make my own input number. However, as I ignore main() to check the first function and find out the result print twice when n_item = 15.

def fun_function(n_items, cost_per_item=27, discount_percent=10, discount_threshold=20):
    """Return the total cost"""
    cost = n_items * cost_per_item  # line 1
    if n_items > discount_threshold:    # line 2
        cost = cost * (1 - discount_percent / 100)  # line 3
        print('{} items cost ${:.2f}'.format(n_items, cost))
    return cost

def main():
    """Compute and print the total cost of a number of items"""
    n_items = int(input("Number of items? "))
    fun_function(n_items, cost_per_item=27, discount_percent=10, discount_threshold=20)

# main()


cost = fun_function(5, 31, 15, 10)
print('5 items cost ${:.2f}'.format(cost))

cost = fun_function(15, 31, 15, 10)
print('15 items cost ${:.2f}'.format(cost))

>>>
5 items cost $155.00
15 items cost $395.25
15 items cost $395.25

Answer 1

You could put the print on the function where you always get a print

    def fun_function(n_items, cost_per_item=27, discount_percent=10, discount_threshold=20):
        """Return the total cost"""
        cost = n_items * cost_per_item  # line 1
        if n_items > discount_threshold:    # line 2
            cost = cost * (1 - discount_percent / 100)  # line 3

        return cost

    def main():
        """Compute and print the total cost of a number of items"""
        n_items = int(input("Number of items? "))
        disc_threshold=10
        cost = fun_function(n_items, cost_per_item=27, discount_percent=10, discount_threshold=disc_threshold)
        if n_items > disc_threshold:
             print('{} items cost ${:.2f}'.format(n_items, cost))

This way if you call:

cost = fun_function(5, 31, 15, 10)

cost = fun_function(15, 31, 15, 10)

>>>
5 items cost $155.00
15 items cost $395.25

You have to make a difference between the behaviour of your function and what you do out of it, like that print, which is not part of the function so it shouldnt be considered as "not expected behaviour".

---EDIT----

If you use the current implementetion written above and run main() and introduce 15, you'll get desired output.