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Parameters

Parameters are pieces of information you can send into a subprogram (like a procedure or function) to help it do its job.

Procedure with parameters

A procedure that displays a message might need a name as a parameter so it can say:
“Welcome, Jamie!”

def welcome_message(name): # name is a formal parameter
    print("Welcome", name)

# Main
welcome_message("Jamie") # "Jamie" is the actual parameter


	
def welcome_message(name): # Formal parameter
    print("Welcome", name)

# Main
customer = "Jamie"
welcome_message(customer) # Actual parameter

Function with parameters

A function that receives numbers as parameters and returns their total.

def add_nums(num1, num2) # Formal parameters
    total = num1 + num2
    return total

# Main
total = add_nums(3,7) # Actual parameters
print(total)


	
def add_nums(num1, num2) # Formal parameters
    total = num1 + num2
    return total

# Main
num1 = 3
num2 = 7
total = add_nums(num1, num2) # Actual parameters
print(total)


	
def add_nums(num1, num2, num3, num4) # Formal parameters
    total = num1 + num2
    return total

# Main
total = add_nums(3,6,2,8) # Actual parameters
print(total)

Formal and actual parameters

Type What it means Where it’s used
Formal parameter A placeholder for a value In the subprogram definition
Actual parameter The real value you pass in When calling the subprogram

Think of formal parameters as empty boxes, and actual parameters as the values that fill them.

Why use parameters?

  • To send information into a subprogram

  • To make subprograms work with different data each time

  • To avoid repeating code by reusing the same subprogram

Key points

  • A subprogram can have one or more parameters

  • Parameters make your code flexible and reusable

  • The order of parameters matters – it must match between the call and the definition