Name reusable code.
Call it when you need it.

Use def, a function name, parentheses, a colon, and indented code to define a reusable action.

01 Learn02 Try03 Predict

01 Learn

A function stores instructions until you call it.

Use def, a function name, parentheses, a colon, and indented code to define a reusable action.

def greet():
    print("Hello from Python!")

greet()
greet()

Defining greet does not run its body. Each greet() call runs the indented print instruction.

Change one value or function call, then explain how the result changes.

↳

Keep this in mind: Read the function definition and its calls before predicting the result.

Try it

def greet():
    print("Hello from Python!")

# Change the message, then call greet more than once
greet()

Run the example, then change one value and observe the result.

02 Try

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03 Predict

What will this program print?

Read the function definition and each call before choosing an answer.

def say_hi():
    print("Hi!")

print("Before")
say_hi()
print("After")

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04 Understanding Check

What will this program print, and what is the difference between defining and calling show_message?

def show_message():
    print("Function body")

print("Defined")
show_message()