Default Values

Part of the Fundamentals section of Coddy's Python journey — lesson 48 of 77.

Sometimes when we create a function, we want to have some arguments that are optional, with predetermined default values.

Example:

def greet(name, greeting="Hello"):
    print(name, greeting)

Using the function with only required argument:

greet("John")
# Output: John Hello

Using the function with both arguments:

greet("john", "welcome")
# Output: john welcome

You can have multiple default arguments:

def describe_person(name, age=25, city="Unknown"):
    print(f"{name} is {age} years old and lives in {city}")

describe_person("Alice")
# Uses both defaults

describe_person("Bob", 30)
# Uses default city

describe_person("Charlie", 35, "New York")
# Uses no defaults

Important Rule: Default arguments must come after non-default arguments in the function definition.
# Correct:
def greet(name, greeting="Hello"):
    print(f"{greeting}, {name}!")
# Incorrect:
def greet(greeting="Hello", name):
    print(f"{greeting}, {name}!")

Cheat sheet

Default arguments in functions:

def greet(name, greeting="Hello"):
    print(name, greeting)

greet("John")  # Output: John Hello
greet("John", "Welcome")  # Output: John Welcome

Multiple default arguments:

def describe_person(name, age=25, city="Unknown"):
    print(f"{name} is {age} years old and lives in {city}")

describe_person("Alice")  # Uses both defaults
describe_person("Bob", 30)  # Uses default city
describe_person("Charlie", 35, "New York")  # Uses no defaults

Important: Default arguments must come after non-default arguments in the function definition.

# Correct:
def greet(name, greeting="Hello"):
    print(f"{greeting}, {name}!")

# Incorrect:
def greet(greeting="Hello", name):
    print(f"{greeting}, {name}!")

Try it yourself

This lesson doesn't include a code challenge.