How to make arguments non-specific in python?

Question

I have a code in python for a pizza shop cost-calculator, which calculates the cost after given an order, which can include pizza, drinks, wings, and coupons. It doesn't necessarily have to have all these arguments, it will have a variety. This is where I'm stuck. I have the code, but I need to use Default-Valued Arguments to make it so that any amount of arguments inserted will produce a valid output. (something about positional arguments)

This is the code:

def pizza_cost(pizorders):
    total = 0
    for order in pizorders:
        total += 13
        if "pepperoni" in order:
            total = total + (x.count("pepperoni") * 1)
        if "mushroom" in order:
            total = total + (x.count("mushroom") * 0.5)
        if "olive" in order:
            total = total + (x.count("olive") * 0.5)
        if "anchovy" in order:
            total = total + (x.count("anchovy") * 2)
        if "ham" in order:
            total = total + (x.count("ham") * 1.5)
    return total

def drink_cost(driorders):
    total = 0
    for order in driorders:
        if order == "small":
            total = total + (x.count("small") * 2)
        if order == "medium":
            total = total + (x.count("medium") * 3)
        if order == "large":
            total = total + (x.count("large") * 3.5)
        if order == "tub":
            total = total + (x.count("tub") * 3.75)
    return total

def wing_cost(wingorders):
    total = 0
    for order in wingorders:
        if order == 10:
            total += 5
        if order == 20:
            total += 9
        if order == 40:
            total += 17.5
        if order == 100:
            total += 48
    return total


def cost_calculator(*pizzas, *drinks, *wings, *coupon):
    total = 0
    total += pizza_cost(pizzas)
    total += drink_cost(drinks)
    total += wing_cost(wings)
    tax = total * 0.0625
    discount = total * coupon
    total += tax
    total -= discount
    return total

And this is the error:

   TypeError                                 Traceback (most recent call last)
~/opt/anaconda3/lib/python3.7/site-packages/bwsi_grader/__init__.py in compare_functions(student, soln, fn_args, fn_kwargs, function_name, comparison_function)
    110     try:
--> 111         student_out = student(*fn_args, **fn_kwargs)
    112     except Exception as e:

TypeError: cost_calculator() missing 3 required positional arguments: 'drinks', 'wings', and 'coupon'

During handling of the above exception, another exception occurred:

StudentError                              Traceback (most recent call last)
<ipython-input-13-322b790cbb8b> in <module>
      1 # Execute this cell to grade your work
      2 from bwsi_grader.python.pizza_shop import grader
----> 3 grader(cost_calculator)

~/opt/anaconda3/lib/python3.7/site-packages/bwsi_grader/python/pizza_shop.py in grader(student_func)
    191     for pizzas, items in zip(std_pizzas, std_orders):
    192         compare_functions(student=student_func, soln=soln,
--> 193                           fn_args=tuple(pizzas), fn_kwargs=items)
    194 
    195     for i in range(1000):

~/opt/anaconda3/lib/python3.7/site-packages/bwsi_grader/__init__.py in compare_functions(student, soln, fn_args, fn_kwargs, function_name, comparison_function)
    111         student_out = student(*fn_args, **fn_kwargs)
    112     except Exception as e:
--> 113         raise StudentError(f"\nCalling \n\t{pad_indent(sig, ln=4)}\nproduces the following error:"
    114                            f"\n\t{type(e).__name__}:{e}"
    115                            f"\nPlease run your function, as displayed above, in your Jupyter "

StudentError: 
Calling 
    student_function([])
produces the following error:
    TypeError:cost_calculator() missing 3 required positional arguments: 'drinks', 'wings', and 'coupon'
Please run your function, as displayed above, in your Jupyter notebook to get a detailed stacktrace of the error, and debug your function.

Answer 1

When you declare a function that does not use default arguments, Python expects you to have necessarily have an input for every parameter. The default argument will allow you to no put something in for an argument.

def cost_calculator(pizza=[], drinks=[], wings=[], coupon=0.0):

     ''' your code here '''

Non-default arguments are called positional arguments because they always have to be entered and must be entered in the right order.

For default arguments, you should make sure that you are entering the name of the argument when making the function call:

cost_calculator(drinks=['small', 'small', 'large'], coupon=0.2)

I think this should work in the grading code. They are using a method called dictionary unpacking that allows you to hand in all your defaulted parameters as a dictionary object that is referred to as kwargs by convention: