Functions: Defining and Calling

Functions let us group reusable code under a name. This makes our code more organized and avoids repetition.

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

Let’s go through the basics of creating and using functions.

1. Defining a Function

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

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

Explanation:

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

2. Calling a Function

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

greet()

Explanation:

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

3. Function with Parameters

Functions can take input values (parameters) to perform different actions based on the input.

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

greet_user("Alice")

Explanation:

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

4. Returning Values

Functions can send back (return) a result using the return statement.

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

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

Explanation:

• 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	Runs the code inside the function
Parameters	Inputs to customize behavior
return	Sends back a value from the function

What’s Next?

Next, you’ll learn how to pass arguments and handle return values in more detail — key to writing powerful Python functions.