Of course, Python comes with a lot of built-in functions. We used `input()`

and `print()`

already. Here are few commonly used built-in functions:

`range()`

– It returns an iterable sequence`open()`

– It opens a file then returns the corresponding file object`sorted()`

– It sorts a list and returns the sorted list`help()`

– It invokes the help system built into Python`abs()`

– Returns the absolute value of a number

## The `range()`

function

The parameter you put in between parenthesis acts like a stop. For example let’s take a look at the following example:

```
for i in range(5):
print(i)
```

It prints all the numbers from 0 to 5 (but not including 5).

If we use it with 2 parameters then we will have something like is shown below:

```
for i in range(2,5):
print(i)
```

It starts printing at number 2 and it stops at 4. Number 5 is not printed.

If we use it with 3 parameters then we will have something like is shown below:

```
for i in range(2,10,3):
print(i)
```

It starts printing with number 2, then prints 5 (which is 2+3 and is less than 10), then prints 8 (which is 5+3 and it is also less than 10). Then it stops printing since the next number would have been 11 and it is out of range.

So, in conclusion, the `range()`

is a general tool that can be used in a variety of contexts. It is commonly used to generate indexes in a `for`

loop but you can use it anywhere you need a series of integers.

```
>>>>>> list(range(5))
[0, 1, 2, 3, 4]
>>> list(range(11, 17))
[11, 12, 13, 14, 15, 16]
>>> list(range(-3, 3, -1))
[]
>>> list(range(3, -3, -1))
[3, 2, 1, 0, -1, -2]
>>> list(range(-3, 3, 1))
[-3, -2, -1, 0, 1, 2]
```

The `range()`

is useful when used within `for`

loops. It is a simple way to repeat an action a specific number of times.

Example:

To print three lines, use `range()`

to generate the appropriate number of integers.

```
>>> for i in range(3):
... print(i, ' developer')
...
0 developer
1 developer
2 developer
```

## The `open()`

function

The `open()`

function opens a file. Let’s modify the file `hello.py`

as shown below:

`print('The message with open()')`

Open the terminal, go to the directory where the file is and type the following commands:

```
f = open(“hello.py”)
f.read(9)
```

This is what the terminal outputs:

It reads the first 9 characters. Of course, you can do many more things with the `open()`

function.

## The `sorted()`

function

The `sorted()`

function does what the name says, it sorts the items of a list for example.

```
>>> a = [5,3,4,2,1]
>>> print sorted(a)
[1, 2, 3, 4, 5]
>>>
```

## The `help()`

function

The `help()`

invokes the help system built into Python. Open the terminal and type `python`

to start Python then type `help()`

. This is what you get:

## The `abs()`

function

The `abs()`

function returns the absolute value of a number. The absolute value of a number is its distance on the numbers line from 0.

Open the terminal and type in the following command:

`abs(-5)`

The terminal will return 5 as you can see below.

The are many more built in functions in Python that you can study and experiment with.