Programming Essentials Python - User Defined Functions - Function Parameters and Arguments

Let us get an overview of different types of Function Parameters and Arguments supported by Python.

  • Parameter is a variable in the declaration of the function. An argument is the actual value of this variable that gets passed to the function.

  • However, in some cases, these two terms are used interchangeably.

  • In Python, parameters can be objects or even functions. We can pass named functions or lambda functions as arguments. We will talk about these details later.

  • Here are different types of parameters or arguments:

    • Parameters with Default Values
    • Varying arguments
    • Keyword arguments
    • Varying Keyword arguments
  • We can pass arguments to a function by parameter position or name. If you use the name, you can pass arguments in any order.

  • You can only specify parameters with default values after mandatory parameters. def get_commission_amount(sales_amount=1000, commission_pct) is syntactically wrong and throws an error.


Let us perform a few tasks to understand more about parameters and arguments with and without default values.

  1. Checking whether phone numbers of a given employee are valid - get_invalid_phone_count

    • Function should take 2 arguments, employee_id and phone_numbers (list)
    • Check whether each phone number has 10 digits.
    • Return employee_id and the number of phone numbers with less than 10 digits
  2. Get commission amount by passing sales amount and commission percentage. However, if the commission percentage is not passed from the caller, then the default percentage should be 10.

def get_invalid_phone_count(employee_id, phone_numbers):
    invalid_count = 0
    for phone_number in phone_numbers:
        if len(phone_number) != 10:
            invalid_count += 1
    return employee_id, invalid_count
s = 'Employee {employee_id} has {invalid_count} invalid phones'

employee_id, invalid_count = get_invalid_phone_count(1, ['1234', '1234567890'])
print(s.format(employee_id=employee_id, invalid_count=invalid_count))

def get_commission_amount(sales_amount, commission_pct=10):
    """Function to compute commission amount. Commission_pct should be passed as percent notation (e.g., 20%)

       20% using percent notation is equal to 0.20 in decimal notation.
    if commission_pct and commission_pct > 100:
        print('Invalid Commission Percentage, greater than 100')
    commission_amount = sales_amount * (commission_pct / 100) if commission_pct else 0
    return commission_amount

# Arguments by position
get_commission_amount(1000, 5)

# Will take commission_pct default value
get_commission_amount(1000, None)
get_commission_amount(1000, 150)

# Arguments by name
get_commission_amount(commission_pct=18, sales_amount=1500)

Summary of the main points discussed in the article. Encourage the reader to practice or engage with the community for further learning.

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