Lesson 9: Functions — Writing Reusable Code

Don't Repeat Yourself. In programming, if you use the same block of code multiple times, it belongs in a function.

A Function is a reusable block of code that performs a specific task. In AI, we use functions for everything from calculating accuracy to processing images.

Defining a Function

You create a function using the def keyword, followed by the function name and parentheses. Inside the parentheses, you define parameters (inputs). The return statement sends a result back.

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

message = greet("AI Learner")
print(message)

Why Functions Matter in ML

Imagine calculating the average error for multiple different models. Instead of writing the math every time, we write an error() function once.

def normalize(value, min_val, max_val):
"""Scales a value to be between 0 and 1."""
return (value - min_val) / (max_val - min_val)

Coding Challenge: The Accuracy Function

Let's write a reusable utility function to calculate classification accuracy.

Define a function called calculate_accuracy that takes two lists as parameters: predictions and actuals.
Inside the function, assume both lists are the same length. Count how many items match at the exact same index. (Hint: use range(len(predictions)) in a loop).
Divide the number of matches by the total number of items to get the accuracy percentage.
return the calculated accuracy.
Call your function with preds = [1,0,1,1] and acts = [1,0,0,1] and print the result.