Python Functions #

A function is a block of organized, reusable code that is used to perform a single, related action. Functions provide better modularity for your application and a high degree of code reusing.

Defining a Function #

You can define a function using the def keyword.

def greet(name):
 """This function greets the person passed in as a parameter."""
 print(f"Hello, {name}!")
# Calling the function
greet("Alice") # "Hello, Alice!"

Arguments #

Information can be passed into functions as arguments. Arguments are specified after the function name, inside the parentheses.

Positional and Keyword Arguments #

def describe_pet(animal_type, pet_name):
 """Display information about a pet."""
 print(f"I have a {animal_type}.")
 print(f"My {animal_type}'s name is {pet_name.title()}.")
# Positional arguments
describe_pet("hamster", "harry")
# Keyword arguments
describe_pet(pet_name="willie", animal_type="dog")

Default Arguments #

def describe_pet(pet_name, animal_type="dog"):
 """Display information about a pet with a default animal type."""
 print(f"I have a {animal_type}.")
 print(f"My {animal_type}'s name is {pet_name.title()}.")
describe_pet("willie") # Uses the default animal_type "dog"

Arbitrary Arguments #

If you do not know how many arguments will be passed into your function, you can use *args for non-keyword arguments and **kwargs for keyword arguments.

def make_pizza(*toppings):
 """Print the list of toppings that have been requested."""
 print(toppings)
make_pizza("pepperoni")
make_pizza("mushrooms", "green peppers", "extra cheese")
def build_profile(first, last, **user_info):
 """Build a dictionary containing everything we know about a user."""
 profile = {"first_name": first, "last_name": last}
 for key, value in user_info.items():
 profile[key] = value
 return profile
user_profile = build_profile("albert", "einstein",
 location="princeton",
 field="physics")
print(user_profile)

Lambda Functions #

A lambda function is a small anonymous function. A lambda function can take any number of arguments, but can only have one expression.

# A lambda function that adds 10 to the number passed in as an argument
x = lambda a: a + 10
print(x(5)) # 15
# A lambda function that multiplies two arguments
multiply = lambda x, y: x * y
print(multiply(5, 6)) # 30