# Python | Functions | Built-in Functions

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”)

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.