What is a function in Python and how do you define it?

A function is a named block of code that can be called multiple times. Functions help avoid duplication and make the code more readable.

Definition and calling:

def greet(name):
    return f"Hello, {name}!"

message = greet("Anna")
print(message)  # Hello, Anna!

Parameters and arguments:

# Default values
def power(base, exponent=2):
    return base ** exponent

power(3)     # 9  (exponent = 2)
power(3, 3)  # 27 (exponent = 3)

Keyword arguments:

def create_user(name, age, city="Moscow"):
    return {"name": name, "age": age, "city": city}

# Keyword arguments can be passed in any order
user = create_user(age=25, name="Anna")

Returning multiple values:

def min_max(numbers):
    return min(numbers), max(numbers)

lo, hi = min_max([3, 1, 7, 2, 9])
print(lo, hi)  # 1 9

Function without return:

If return is absent, the function returns None:

def say_hello(name):
    print(f"Hello, {name}!")

result = say_hello("World")
print(result)  # None