Functions

You've been using functions all month without building one. print(), len(), int(), input() — each is a named piece of work somebody else wrote.

Now you write your own:

def greet(name):
    print("Hello,", name + "!")

greet("Ananya")
greet("Bilal")

def defines it. The name is yours. The brackets hold whatever information it needs. Write it once, call it as often as you like.

A function takes information in and can hand a result back:

def calculate_average(marks):
    total = sum(marks)
    return total / len(marks)

class_a = [85, 92, 78]
print(calculate_average(class_a))

• marks is a parameter — information going in
• return sends a value back to whoever called it

The difference between print and return matters: print shows a value to a human; return hands it back to the program so it can be stored or used in further calculation. A function that prints when it should return can't be built on.