Functions: Defining and Calling

Functions let you group reusable code under a single name. This makes your programs cleaner, easier to read, and free of repetition.

In Python, you define a function using the def keyword, followed by the function name and parentheses.

1. Defining a Function

Use def to define a function. Add parentheses (with or without parameters) and end the line with a colon (:).

Defining a Function

def greet():
    print("Hello, welcome!")

• The function is named greet.
• It has no parameters.
• When called, it prints a greeting.

2. Calling a Function

Once defined, you can call the function by writing its name followed by parentheses.

Calling a Function

greet()

• This line runs the greet() function and prints the message.

3. Function with Parameters

Functions can accept input values, known as parameters, to perform actions that depend on those inputs.

Function with Parameters

def greet_user(name):
    print("Hello,", name)

greet_user("Alice")

• greet_user takes one argument called name.
• When called with "Alice", it prints: Hello, Alice.

4. Returning Values

Functions can produce and send back results using the return statement.

Returning Values

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

result = add(5, 3)
print(result)

• add takes two arguments and returns their sum.
• The result is stored in result and printed.

Summary

Concept	Description
def	Keyword to define a function
Function call	Executes the code inside the function
Parameters	Inputs to customize behavior
return	Sends back a value to the caller

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