Functions play an important role in Python programming. With a function, you can name a logical entity that performs a specific action. Arguments can be passed to a function to control its execution. The code inside a function is executed only when the function is called.

Functions are important because they help in reducing code repetition. If the same operation needs to be performed multiple times in a program, it is advisable to write that operation as a function, which can then be called at different points in the program. This reduces the amount of code to be written and makes the program easier to maintain.

In Python, functions are defined using the 

 keyword, followed by the function name and any arguments. The function code is written indented on the following lines.

Example of a function that calculates the sum of two numbers:

In this function there are two arguments, 

. Inside the function the sum of the arguments is calculated and saved in the variable 

Functions can return or not return values. For example, the function "tallenna_peli" may not return anything, it just saves the game. But the function "summa" (like the example above) is logically expected to return the summed total to the function caller.

Functions in Python return a value with the 

 keyword. After that, the execution of the function ends, and no more lines of code inside the function are executed. The return statement can also be made without any arguments, which terminates the function execution without a return value.

The function is called by giving the function name and arguments in parentheses. For example, the above function could be called as follows:

, because the result returned by the function 

 is saved in the variable result and then printed with the 

 that accepts a list of numbers and returns the largest number. You can assume that the list contains at least one number.

An example of how the function should work:

Write a function named suurin_luku that accepts numbers from a list and returns the largest number. You can assume that the list contains at least one number.

Write a function

## What are functions?

Functions play an important role in Python programming. With a function, you can name a logical entity that performs a specific action. Arguments can be passed to a function to control its execution. The code inside a function is executed only when the function is called.

---

## What functions are needed?

Functions are important because they help in reducing code repetition. If the same operation needs to be performed multiple times in a program, it is advisable to write that operation as a function, which can then be called at different points in the program. This reduces the amount of code to be written and makes the program easier to maintain.

---

## Python functions

In Python, functions are defined using the **def** keyword, followed by the function name and any arguments. The function code is written indented on the following lines.

Example of a function that calculates the sum of two numbers:

```python
def sum(a, b):
    result = a + b
    return result

```

In this function there are two arguments, **a** and **b**. Inside the function the sum of the arguments is calculated and saved in the variable **result**. Finally, the *result* is *returned* as the result of the function.

---

## Function return values

Functions can return or not return values. For example, the function "tallenna\_peli" may not return anything, it just saves the game. But the function "summa" (like the example above) is logically expected to return the summed total to the function caller.

Functions in Python return a value with the **return** keyword. After that, the execution of the function ends, and no more lines of code inside the function are executed. The return statement can also be made without any arguments, which terminates the function execution without a return value.

---

## Calling a function

The function is called by giving the function name and arguments in parentheses. For example, the above function could be called as follows:

```python
result = sum(2, 3)
print(result)
```

This would print **5**, because the result returned by the function **sum(2, 3)** is saved in the variable result and then printed with the **print** function.

---

## 
Exercise

Write a function named **largest\_number** that accepts a list of numbers and returns the largest number. You can assume that the list contains at least one number.

An example of how the function should work:

```python
Reading List = [3, 7, 1, 9, 4]
print(largest_number(numberlist)) # Prints 9
```

@exercise bb75cc4239ae


Functions

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Functions

What are functions?

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