Parameters and Arguments

15 min · Beginner

Python offers tremendous flexibility when passing inputs to functions. You can pass arguments by position or explicitly by name (keyword arguments).

Positional arguments

Positional argument is a value passed to a function by its place in the call. The first value goes to the first parameter, the second to the second, and so on.

By default, arguments match parameters based on their order in the function call.

Python

def format_name(first, last):    return f"{last}, {first}"
print(format_name("Sunita", "Sharma"))

Example 1 · Position decides the meaning

Python

def order_line(product, quantity, price):    print(f"{quantity} x {product} at {price} = {quantity * price}")
order_line("Keyboard", 2, 1500)order_line("Keyboard", 1500, 2)

Output

2 x Keyboard at 1500 = 3000
1500 x Keyboard at 2 = 3000

What this code does

The first call matches by position: quantity is 2 and price is 1500.
The second call swaps the numbers. Python does not complain, but the line now says 1500 x Keyboard at 2.

Because 'Sunita' was passed first, it binds to first. 'Sharma' binds to last.

Keyword arguments

Keyword argument is a value passed with the parameter's name, as in role="Admin". Keyword arguments can come in any order.

You can explicitly specify the parameter name during the call: param=value. Order does not matter when using keyword arguments.

Python

def create_user(username, email, role):    return f"{username} ({role}) <{email}>"
print(create_user(role="Admin", username="arun", email="arun@work.com"))

Example 2 · Names make the call safe

Python

def order_line(product, quantity, price):    print(f"{quantity} x {product} at {price} = {quantity * price}")
order_line(price=1500, product="Keyboard", quantity=2)order_line("Mouse", quantity=3, price=400)

Output

2 x Keyboard at 1500 = 3000
3 x Mouse at 400 = 1200

What this code does

Keyword arguments can come in any order because each one names its parameter.
A call may start with positional values and then continue with keywords. Never put a positional value after a keyword.

Keyword arguments make function calls self-documenting and prevent bugs caused by swapped arguments.

Returning multiple values

Tuple unpacking assigns the items of a returned tuple to separate variables in one line, such as low, high = get_min_max(values).

In Python, a function can return several values separated by commas. Python bundles them into a tuple (see Tuples (opens in a new tab)), which you can unpack straight into variables.

Python

def get_min_max(a, b, c):    return min(a, b, c), max(a, b, c)
low, high = get_min_max(12, 45, 8)print(f"Lowest: {low}, Highest: {high}")

Example 3 · Quotient and remainder

Python

1def divide_with_remainder(dividend, divisor):2    quotient = dividend // divisor3    remainder = dividend % divisor4    return quotient, remainder5
6q, r = divide_with_remainder(17, 5)7print(f"Quotient: {q}, Remainder: {r}")

Output

Quotient: 3, Remainder: 2

What this code does

Calculates quotient ($17 // 5 = 3$) and remainder ($17 % 5 = 2$).
Returns both values as a tuple and unpacks them into q and r.

Example 4 · One tuple, then three names

Python

1def summary(a, b, c):2    total = a + b + c3    return total, total / 3, max(a, b, c)4
5result = summary(70, 80, 90)6print(result)7total, average, best = result8print(total, average, best)

Output

(240, 80.0, 90)
240 80.0 90

What this code does

Printing result shows it is a single tuple: (240, 80.0, 90).
Unpacking needs exactly as many names as the tuple has items.

low receives 8 and high receives 45 via automatic tuple unpacking.

Next step

Check your understanding

9 quick questions

def order_line(product, quantity, price): print(f"{quantity} x {product} at {price} = {quantity * price}") order_line(price=1500, product="Keyboard", quantity=2)order_line("Mouse", quantity=3, price=400)

Returning multiple values

Tuple unpacking assigns the items of a returned tuple to separate variables in one line, such as low, high = get_min_max(values).

In Python, a function can return several values separated by commas. Python bundles them into a tuple (see Tuples), which you can unpack straight into variables.

1def divide_with_remainder(dividend, divisor):2 quotient = dividend // divisor3 remainder = dividend % divisor4 return quotient, remainder5 6q, r = divide_with_remainder(17, 5)7print(f"Quotient: {q}, Remainder: {r}")