Python is a versatile programming language that provides a wide range of built-in functions as well as the ability to define your own functions. Functions in Python are blocks of reusable code designed to perform a specific task. Here, I'll cover some important aspects of Python functions:
Defining Functions:

You can define a function using the def keyword, followed by the function name and a colon. The function body is indented.

python

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

# Function call
greet("John")

Function Parameters:

Functions can take parameters (input values) to perform operations. Parameters are specified within the parentheses.

python

def add_numbers(a, b):
"""This function adds two numbers."""
return a + b

result = add_numbers(3, 5)
print(result) # Output: 8

Default Parameters:

You can provide default values for function parameters.

python

def power(base, exponent=2):
"""This function calculates the power of a number."""
return base ** exponent

print(power(3)) # Output: 9 (3^2)
print(power(3, 3)) # Output: 27 (3^3)

Return Statement:

Functions can return values using the return statement. If no return statement is encountered, the function returns None by default.

python

def square(x):
"""This function returns the square of a number."""
return x ** 2

result = square(4)
print(result) # Output: 16

Docstrings:

You can provide documentation for your functions using docstrings. Docstrings are triple-quoted strings at the beginning of a function.

python

def multiply(a, b):
"""This function multiplies two numbers.

Parameters:
a (int): The first number.
b (int): The second number.

Returns:
int: The product of a and b.
"""
return a * b

Variable Scope:

Variables defined inside a function are local to that function unless explicitly declared as global. Variables outside functions are global.

python

global_variable = 10

def my_function():
local_variable = 5
print(global_variable) # Accessing global variable is okay
print(local_variable) # Accessing local variable

my_function()
print(global_variable) # Accessing global variable outside the function is okay
# print(local_variable) # This would raise an error as local_variable is not defined outside the function

These are some fundamental aspects of functions in Python. Understanding these concepts will help you write modular and reusable code.