session-05

Session 05: Functions, Strings and Lists

Functions

Quick review notes on functions.

Void (Non Fruitful) Functions

• Do not return a value

def welcome():
    print("-" * 50)
    print("Welcome to this demo")
    print("-" * 50)


welcome()

Code: functions_void.py

Functions with (Positional) Parameters

• Define one or more parameters
• Accepts exactly the same number of arguments
• Each argument must match the parameter in the same position
• If number of arguments does not match number of parameters then an error will occur

def welcome(persons_name):
    print("-" * 50)
    print(f"Welcome to this demo, {persons_name}")
    print("-" * 50)

Calling welcome, and missing the argument:

welcome()

Gives output of:

Traceback (most recent call last):
  File "C:\Users\5001775\Source\Repos\ICTPRG302\Sessions\session-05\functions_with_parameter.py", line 26, in <module>
    welcome()  # ERROR! missing the argument
    ^^^^^^^^^
TypeError: welcome() missing 1 required positional argument: 'persons_name'

Note: This tells us we are missing an argument for persons_name. It tells us that the error is most likely at line 26 of our code.

Code: functions_with_parameter.py

Functions with Named Parameters

• Naming parameters allows for default values
• Naming parameters allows for arguments to be reordered

def welcome(person=""):
    print("-" * 50)
    print(f"Welcome to this demo, {person}")
    print("-" * 50)


welcome()
welcome("Janette")
welcome(person="Jill")

Code: functions_with_named_parameter.py

Functions with Named & Positional Parameters

• Naming parameters allows for default values
• Naming parameters allows for arguments to be reordered
• Named parameters must come after positional parameters

def welcome(person, character="-"):
    # Welcome has positional (person) and named (character) parameters
    print(character * 50)
    print(f"Welcome to this demo, {person:>10s}")
    print(character * 50)


welcome("Janette")
welcome("Jack", "=")
welcome("James", "")
welcome("Jill", character="*") 

Code: functions_with_positional_and_named_parameter.py

Small change in this example - both parameters are named.

def welcome(person="", character="-"):
    print(character * 50)
    print(f"Welcome to this demo, {person}")
    print(character * 50)


welcome()
welcome("Janette")
welcome("Josiah", "#")
# Cannot use welcome(person="Eve","%") as named parameters must be last
welcome("Stacey", character="*")
welcome(person="Bradley", character="=")

Code: functions_with_multiple_named_parameters.py

Functions that return results (Fruitful)

• usually have at least one parameter
• return (usually) one result

Example calculates the total cost of a product given the weight and the price per kilogram.

def cost(quantity=0.0, price=0.0):
    total_cost = quantity * price
    return total_cost

weight = 3.5
price_per_kilo = 3.35

total = cost(weight, price_per_kilo)
print(f"Total: ${total:1.2f}")

total_for_apples = cost(price=5.56, quantity=9)
print(f"Total: ${total_for_apples:4.2f}")

Code: functions_with_parameter_and_result.py