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 define a function using the def keyword, followed by a function name, parentheses, and a colon. Inside the parentheses, you can pass zero or more parameters. Here's a basic example:
def greet():
print("Hello, welcome to the tutorial!")
greet()
Hello, welcome to the tutorial!
Passing Parameters¶
Functions become more flexible when parameters are involved. Parameters are variables passed into the function. Here's how to use them:
def greet(name):
print(f"Hello, {name}! How are you today?")
greet("Alice")
Hello, Alice! How are you today?
Return Values¶
To let a function return a result, use the return statement. It exits the function and optionally passes back an expression to the caller:
def add_numbers(x, y):
return x + y
result = add_numbers(5, 3)
print("The sum is:", result)
The sum is: 8
Default Parameter Values¶
You can set default values for parameters, which will be used if no argument is passed:
def greet(name, message="Good morning!"):
print(f"Hello, {name}. {message}")
greet("Bob")
greet("Bob", "How was your day?")
Hello, Bob. Good morning! Hello, Bob. How was your day?
Keyword Arguments¶
When you call a function, you can specify the arguments by naming them. This allows for more readable code and skipping some arguments if defaults are set:
def describe_pet(animal, name):
print(f"I have a {animal} named {name}.")
describe_pet(name="Whiskers", animal="cat")
I have a cat named Whiskers.
Arbitrary Arguments¶
If you don't know how many arguments will be passed into your function, add a * before the parameter name in the function definition. This way the function will receive a tuple of arguments:
def make_pizza(*toppings):
print("Making a pizza with the following toppings:")
for topping in toppings:
print(f"- {topping}")
make_pizza('pepperoni')
make_pizza('mushrooms', 'green peppers', 'extra cheese')
Making a pizza with the following toppings: - pepperoni Making a pizza with the following toppings: - mushrooms - green peppers - extra cheese
Recursive Functions¶
A function can call itself, known as recursion. Here’s a simple example using factorial:
def factorial(n):
if n == 1:
return 1
else:
return n * factorial(n-1)
print(factorial(5))
120
Lambda Functions¶
Lambda functions are small anonymous functions defined with the lambda keyword. They can have any number of arguments but only one expression:
square = lambda x: x ** 2
print(square(5))
25