Function Parameters and Arguments¶

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

Parameter is variable in the declaration of function. Argument is the actual value of this variable that gets passed to 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 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 error.

Tasks¶

Let us perform a few tasks to understand more about parameters and arguments with and with out default values.

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 have 10 digits.
- Return employee_id and number of phone numbers with less than 10 digits
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} have {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))

Employee 1 have 1 invalid phones

def get_commission_amount(sales_amount=1000, commission_pct):
    """Function to compute commission amount. commission_pct should be passed as percent notation (eg: 20%)
       20% using percent notation is equal to 0.20 in decimal notation.
    """
    commission_amount = (sales_amount * commission_pct / 100) if commission_pct else 0
    return commission_amount

  File "<ipython-input-5-60598743caf3>", line 1
    def get_commission_amount(sales_amount=1000, commission_pct):
                             ^
SyntaxError: non-default argument follows default argument

def get_commission_amount(sales_amount, commission_pct=10):
    """Function to compute commission amount. commission_pct should be passed as percent notation (eg: 20%)
       20% using percent notation is equal to 0.20 in decimal notation.
    """
    if commission_pct and commission_pct > 100:
        print('Invalid Commision Percentage, greater than 100')
        return
    commission_amount = sales_amount * (commission_pct / 100) if commission_pct else 0
    return commission_amount

# Arguments by position
get_commission_amount(1000, 5)

50.0

# Will take commission_pct default value
get_commission_amount(1000)

100.0

get_commission_amount(1000, None)

get_commission_amount(1000, 150)

Invalid Commision Percentage, greater than 100

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

270.0

Mastering Python

Function Parameters and Arguments¶

Tasks¶