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# Example 1: A basic greeting function
def say_hello():
    print("Hello there!")

say_hello()

# Separator line
print('=' * 40)

# Example 2: A function with parameters
def greet_user(name):
    print("Hi", name + "!")

greet_user("Ella")
greet_user("Sam")

# Separator line
print('=' * 40)

# Example 3: A function that returns a value
def square(number):
    return number * number

result = square(4)
print("4 squared is", result)

# 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.

```python
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.

```python
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.

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

```python
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.

```python
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.

In Python, the 'def' keyword is used to define functions, making your code reusable and modular. Functions are named blocks of code that can be executed whenever needed, helping to organize and simplify your programming tasks.

### In Python, functions are defined using the 'def' keyword followed by the function name and parentheses.

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