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

say_hello()

print('=' * 40)

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

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

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 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 (`:`).

```python title="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.

```python title="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.

```python title="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.

```python title="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 |

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	Executes the code inside the function
Parameters	Inputs to customize behavior
`return`	Sends back a value to the caller

Functions: Defining and Calling

1. Defining a Function

2. Calling a Function

3. Function with Parameters

4. Returning Values

Summary

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

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