Parameters and return

Functions get really useful when you can feed them data and get an answer back. That's what parameters and return are for.

Parameters: passing data in

List parameters inside the parentheses. They act like variables the caller fills in:

Python

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

greet("Alice")   # Hello, Alice
greet("Sam")     # Hello, Sam

You can have more than one parameter, separated by commas:

Python

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

add(2, 3)   # 5

return: sending a value back

print only shows text on screen. To send a value back to the caller so it can be reused, use return:

Python

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

result = add(2, 3)
print(result)        # 5
print(add(10, 5))    # 15

The difference matters: a function that prints just displays something, while a function that returns hands you a value you can store, print, or use in more math.

Key takeaways

Parameters go in the parentheses and let the caller pass data in.
return sends a value back so the caller can use the result.
print shows text; return gives you a value to work with.