Learn Combination of Positional and Keyword Arbitrary Arguments

Section 3. Chapter 3

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Consider a function that calculates the total cost of multiple items while allowing you to pass any number of prices and optional keyword settings such as discounts or taxes.


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def calculate_total_cost(*prices, **settings):
    subtotal = sum(prices)
    discount = settings.get('discount', 0)
    tax = settings.get('tax', 0)
    
    discount_amount = subtotal * (discount / 100)
    taxed_amount = (subtotal - discount_amount) * (1 + tax / 100)
    
    print(f'Subtotal: ${subtotal:.2f}')
    
    if discount > 0:
        print(f'Discount: {discount}% (-${discount_amount:.2f})')
    else:
        print('No discount applied.')
    
    if tax > 0:
        print(f'Tax: {tax}% (+${taxed_amount - (subtotal - discount_amount):.2f})')
    
    print(f'Final total: ${taxed_amount:.2f}')
    print()

# Examples of using the function
calculate_total_cost(1000, 250, 50)
calculate_total_cost(1200, 800, discount=10)
calculate_total_cost(500, 750, 250, discount=5, tax=8)

In the code above, you will notice the line settings.get('discount', 0). Because settings collects keyword arguments into a standard Python dictionary, you use the dictionary .get() method to retrieve values safely.

Normally, if you try to look up a key that doesn't exist in a dictionary using square brackets (like settings['discount']), Python will crash and throw a KeyError. The .get() method prevents this by allowing you to provide a fallback default value.

The syntax works like this:

dictionary.get(key, default_value)

key: the name of the setting you are looking for (e.g., 'discount' or 'tax').
default_value: the value to return if that key was not passed into the function.

Rules for Combining Arbitrary Arguments

Positional Arbitrary Arguments (`*args`)

*args collects all extra positional arguments into a tuple. In this example, the function can take any number of item prices without needing to define them explicitly.

For example:

calculate_total_cost(500, 250, 100)

Here, *prices becomes (500, 250, 100).

Keyword Arbitrary Arguments (`**kwargs`)

**kwargs collects all named (keyword) arguments into a dictionary. This allows the function to accept additional named settings such as discount or tax, even if they weren’t predefined.

For example:

calculate_total_cost(1000, 500, discount=10, tax=5)

Here, **settings becomes {'discount': 10, 'tax': 5}.

Combining Both

You can use both *args and **kwargs in the same function to achieve maximum flexibility — letting you handle any number of positional values and any combination of named settings.

Note

Always place *args before **kwargs in the function signature – reversing the order will result in a SyntaxError.

Task

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Implement a generate_report function that accepts any number of numeric scores and optional keyword settings.

Use *args to collect scores (name the parameter scores) and **kwargs to collect optional settings.
Calculate the average of all provided scores by summing all values in scores and dividing by the number of scores:
$\text{Average} = \frac{\text{sum}(scores)}{\text{len}(scores)}$
If a 'label' key is present in **kwargs, use its value as the report title; otherwise use 'Report'.
If a 'passing_score' key is present in **kwargs, check whether the average meets or exceeds it:
- If yes, add 'Status: Pass' to the report.
- If no, add 'Status: Fail'.
Return the result as a formatted string: '{label} | Average: {avg:.2f} | {status}'. If no 'passing_score' is provided, omit the status part: '{label} | Average: {avg:.2f}'.

Solution

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Section 3. Chapter 3

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Combination of Positional and Keyword Arbitrary Arguments

Rules for Combining Arbitrary Arguments

Positional Arbitrary Arguments (*args)

Keyword Arbitrary Arguments (**kwargs)

Combining Both

Solution

Positional Arbitrary Arguments (`*args`)

Keyword Arbitrary Arguments (`**kwargs`)