# List in python A list in python is an ordered set in which each of its values is represented by an index. These values are termed elements. A list is like a string, which is an ordered set of characters.

## How to Create List?

In lists, the elements can be of any type. These ordered sets like List or string are called sequences.

Examples:

There are various ways to create a list.

([ these brackets are used ] ) (“[ ]”)

• [ 1, 2, 3, 4, 5 ] – It’s a list of five integers
•  [ “book”, “pen”, “eraser”, “chalk” ] – it’s a list of four stationary items.

### Nested List in python:

One list can hold another list i.e Nested List

Example :

``["batman", 1, [2, 9], 3.7] ``

## Consecutive Integers:

Lists handles the consecutive integers in an ease in python.

Example:

``[1, 2, 3, 4, 5] → range(1, 5) ``

This range function consists of two arguments and delivers a list holding integers from first argument to second argument.

Note: The first argument is included in the list whereas the second argument is excluded. Others types of Range Function. The range has two other forms as well.

## Three Arguments Range:

The third parameter gives the gap between two successive values (also called Step Size)

Let’s understand by an example: range(2, 12, 2)

This gives us the list as  : [2, 4, 6, 8, 10]

• Single Argument : It creates a list that starts from 0.

Example:

`` [0, 1, 2, 3, 4]``

### Empty List in python:

It does not contain any value. It is represented by [].

So now we have created our list and we will pass them as an argument to the functions.

Let’s understand it by few examples:

``````room = [“fan”, “sofa”, “bed”]
Sum = [13, 14]
Print Sum, room
``````

## How to Access the Elements

The syntax is same as the syntax for accessing the characters of a string using the bracket operator ( [] ). Index is represented inside the brackets.

Note: Indices begin from 0.

Example:

``````print sum

``````

The bracket operator can be used anywhere in the expression.

We use loops to access the index

`````` room = ["sofa", "bed", "pillow", "canvas"]
i = 0        // It will iterate for 4 times i.e. 0, 1, 2 and 3 and then it fails
while i < 4:
print room[i]
i = i + 1
``````

### Operations in List

The + operator: It concatenates the list.

``````x = [2,4,6]
y = [1,3,5]
z = x + y
print z

``````

Output

``=> [2, 4, 6, 1, 3, 5]``

* operator: It gives the number of time the value needs to be repeated.

Example:

`````` * 4
# output
→ [1, 1, 1, 1]

[2, 4, 6] * 2
# output
→ [2, 4, 6, 2, 4, 6]
``````

### List Slices in python

It works well with lists. Let us understand with

example.

``````num = ['1', '2', '3', '4', '5', '6']
→ list[1 : 4]
['2', '3', ‘4’, ‘5’]

→ list[ :4 ]
['0', '1', '2', '3']

→ list[ 3: ]
['4', '5', '6']

→  list[ : ]
['1', '2', '3', '4', '5', '6']
``````

### Mutable Lists in python

Lists are mutable in nature, which means that we can change their elements.

``````country = ["India", "France", "Italy"]
>>> country = "USA"
>>> country = "Sudan"
>>> print county  → ['USA', 'France', 'Sudan']

``````

We can update several elements at a time.

Example:

``````list = ['1', '2', '3', '4', '5', '6']
list[1 : 3] = ['a', 'b']
print list
['1', 'a', 'b', '4', '5', '6']
``````

We can likewise expel components from a list by allotting the vacant list to them.

Example:

``````list = ['1', '2', '3', '4', '5', '6']
list[1 : 3] = []
print list ['1', '4', '5', '6']
``````

### List Deletion in python

It is an alternative to slice which can be error-prone. del function removes an element from a list.

Example:

``````a = ['a', 'b', 'c']
del a
print a
→['a', 'c']
``````

del can handle negative indices and may lead to runtime error if the index is out of range.