Defining a Function

Lesson

Defining a Function

A function is a named block of code. You define it once and run it as many times as you want.

def greet():
    print("Hello")
    print("Welcome aboard")

def starts the definition. greet is the function's name. The parentheses and colon are required. Every indented line below the def line belongs to the function — this indented block is the function's body.

Defining a function does not run it. To run it, call it by writing its name followed by parentheses:

def greet():
    print("Hello")
    print("Welcome aboard")

greet()
greet()

Output:

Hello
Welcome aboard
Hello
Welcome aboard

The body ran twice — once per call. A function must be defined before the line that calls it.

Exercise

Define a function named say_hello that prints exactly one line:

Hello!

Below the definition, call it once.

Run your code to see the output, then press Submit.

Tests

import io
import unittest
from contextlib import redirect_stdout


class TestShowWelcome(unittest.TestCase):
    def test_say_hello_prints_hello(self):
        captured = io.StringIO()
        with redirect_stdout(captured):
            say_hello()
        self.assertEqual(captured.getvalue(), "Hello!\n")

Solution

def say_hello():
    print("Hello!")


say_hello()

Solution hidden. Give it a real try first.

Discussion

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main.py

Console

Press Run to execute your code, or Submit to test and complete this problem.