Card 13: Parameters

Module 5: Reusable Code

1 The Hook

A function is like a Vending Machine.

Input (Parameters): Money + Button Press.
Process: Machine checks money, finds item.
Output (Return): The snack drops out.

Start thinking: Input -> Function -> Output.

2 Worked Example

A machine that adds two numbers.

# Input goes in brackets (a, b)

def add_machine(a, b):

# Output comes out

return a + b

# Use it

result = add_machine(5, 10)

print(result) # Prints 15

PREDICT

What does this machine return?

def magic(x):
return x * x

print(magic(5))

Interactive Editor

main.py

def calc_cost(price):
    tax = price * 0.2
    return price + tax

# Buying a £10 item
total = calc_cost(10)
print(total)

Terminal Output

> _

BRONZE (MODIFY)

🥉 Username Creator

1. Look at make_user. It currently just returns "FirstName".
2. Modify it to return first + last (Combine them).
3. Test it.

bronze.py

def make_user(first, last):
    return first

# Should print: BondJames
print(make_user("Bond", "James"))

> _

SILVER (FIX)

🥈 Broken Calculator

This subtraction machine needs TWO numbers (inputs), but the lazy user only gave one!
1. Run it to see the error.
2. Fix the line subtract(10) by adding a second number, e.g., subtract(10, 3).

silver.py

def subtract(a, b):
    return a - b

# ERROR HERE: Missing Input!
print(subtract(10))

> _

GOLD (MAKE)

🥇 Area Factory

1. Define function calculate_area(w, h).
2. Return w * h.
3. Print the area of a 5x5 square.

gold.py

def ...
    return ...

print(...)

> _

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