Defining and Calling Functions in Python

What is a Function in Python?

A function in Python is defined using the def keyword, followed by:

• The function name

• A list of parameters inside parentheses ()

• An indented code block that forms the function’s body

Example: Simple Function

def greet(name, age):
    """Print a greeting with a name and age."""  # This is a docstring
    print(f"{name} is {age} years old.")

# Calling the function
greet("Alice", 21)

Output:

Alice is 21 years old.

Explanation of the Example

• Function Name: greet

• Parameters: name and age

• Function Body: The indented print() line

• Function Call: greet("Alice", 21)

Here, we pass "Alice" and 21 as arguments to the greet function, which then executes and prints the greeting.

How Function Definition Works

• The def keyword introduces the function.

• The first indented line can be a docstring (optional), which describes what the function does.

• The rest of the indented code is the function body.

• Defining a function creates a function object and assigns it to the function name.

You can even assign a function to another variable:

say_hello = greet
say_hello("Bob", 30)

How to Call a Function

To call a function:

• Use its name followed by parentheses ()

• Pass arguments inside the parentheses if required

Example:

greet("Alice", 21)

Flow of Function Execution

When a function is called:

1. Python jumps to the function definition

2. Executes the body of the function

3. Returns control to the point where the function was called

Example: Function that Returns a Value

def add(a, b):
    return a + b

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

• add is a function that returns the sum of a and b

• add(5, 3) returns 8, which we store in result and print

Why Use Functions?

• Avoid code repetition

• Make programs more organized and modular

• Improve code readability and reusability