Use parameters

What are Parameters?

Think of a parameter as a placeholder in a recipe. The recipe (function) tells you how to make a dish, but the exact ingredients (values) can change each time you cook. In programming, a parameter is a variable that receives a value when a function is called. 📚

Why Use Parameters?

• Reusability – Write a function once, use it many times with different data.
• Modularity – Break complex tasks into smaller, manageable parts.
• Clarity – Parameters make it clear what data a function needs.

Defining Parameters in Python

In Python, you define parameters inside the parentheses of a function definition:

def greet(name):
    print(f"Hello, {name}!")
  

Here, name is a parameter. When we call greet("Alice"), name receives the value "Alice".

Example: A Simple Calculator

Let’s build a function that adds two numbers. The numbers are parameters, so we can add any pair of numbers we like.

def add(a, b):
    return a + b

result = add(5, 7)   # result is 12
  

The add function can now be used for any two numbers, not just 5 and 7. 🎲

Parameters vs. Arguments

Exam Tip Box

📌 Remember: When writing a function, list the parameters in the order they are needed. In the exam, you may be asked to write a function that takes two parameters and returns their product. Make sure you include the return statement – otherwise the function will return None by default.

📌 Tip: Use descriptive parameter names like length or radius instead of single letters. This makes your code easier to read and less error‑prone.

Advanced: Default Parameters

You can give a parameter a default value. If the caller does not provide that argument, the default is used.

def greet(name="Student"):
    print(f"Hello, {name}!")

greet()          # prints "Hello, Student!"
greet("Bob")     # prints "Hello, Bob!"
  

This is handy for optional features or when you want a sensible default. 🎯

Mathematical Example with LaTeX

Suppose we want a function that calculates the area of a circle. The formula is:

$$A = \pi r^2$$

In code, r is a parameter:

import math

def circle_area(radius):
    return math.pi * radius ** 2
  

Call circle_area(3) to get the area for a radius of 3 units.

Practice Exercise

1. Create a function multiply(a, b) that returns the product of two numbers.
2. Test it with the pairs (4, 5) and (7, 0).
3. Modify the function to use a default value of 1 for b.

Try to write the function with clear, descriptive names and include a return statement. Good luck! 🚀