Defining and Calling Functions in Python
Functions are reusable blocks of code that perform a specific task. They help in organizing code, improving readability, and reducing redundancy.

1. Defining a Functions:
A function is defined using the def keyword, followed by a function name and parentheses. It can take parameters and return a value.

Syntax:
def function_name(parameters):
   """Optional docstring describing the function"""
   # Function body
   return value  # (optional)

2. Calling a Function:
A function is called by using its name followed by parentheses. If the function accepts arguments, values must be passed inside the parentheses.

Syntax:
function_name(arguments)

Examples of Function Usage

Example 1 : Function Without Parameters 
def greet():
   print("Hello! Welcome to Python functions.")

# Calling the function
greet()

Output:
Hello! Welcome to Python functions.

Example 2 : Function with Parameters
def add_numbers(a, b):
   return a + b

# Calling the function with arguments
result = add_numbers(5, 3)
print("Sum:", result)

Output:
Sum: 8

Example 3 : Function with Default Parameters
def greet(name="Guest"):
   print(f"Hello, {name}!")

# Calling the function without an argument
greet()

# Calling the function with an argument
greet("Alice")

Output:
Hello, Guest!  
Hello, Alice!

Example 4 : Function Returning Multiple Values 
def calculate(a, b):
   sum_result = a + b
   diff_result = a - b
   return sum_result, diff_result

# Calling the function
sum_val, diff_val = calculate(10, 4)
print("Sum:", sum_val)
print("Difference:", diff_val)

Output:
Sum: 14  
Difference: 6

Key Benefits of Using Functions
- Code Reusability - Write once, use multiple times.
- Modularity - Breaks complex problems into smaller functions.
- Improved Readability - Organized and structured code.
- Easier Debugging - Isolate issues in specific functions.

Functions are fundamental in Python programming, allowing for effcient and scalable code development.