Python Collections – Arrays

  

Collection means storage location of number of values in same named space location.

 

There are four collection data types in the Python programming language:

•           List is a collection which is ordered and changeable. Duplicate elements can be stored in list. 

•           Tuple is a collection which is ordered and unchangeable. It also allows duplicate elements. 

•           Set is a collection which is unordered and unindexed. Duplicate elements not allowed here. 

•           Dictionary is a collection which is unordered and changeable. Duplicate elements not allowed here. 

 

Python Lists

 Lists are used to store multiple items in a single variable. Lists are created using square brackets:

 Example

Create a List:

  mylist = ["Assam", "Benaras", "Chennai"]

print( mylist)

 Output will be: = [‘Assam’, ‘Benaras’, ‘Chennai’]

 

List with duplicate values

Example

Lists allow duplicate values:

  mylist = ["Assam", "Benaras", "Chennai", “Assam”]

print( mylist)

Output will be: = [‘Assam’, ‘Benaras’, ‘Chennai’, ‘Assam’]

 

 List Length

To determine how many items a list has, use the len() function:

 Example

Print the number of items in the list: 

 mylist = ["apple", "banana", "cherry"]

print(len( mylist))

 Output would be: 3

 

List Items - Data Types

 List items can be of any data type:

 Example

String, int and boolean data types:

 list1 = ["Assam", "Benaras", "Chennai"]

list2 = [1, 5, 7, 9, 3]

list3 = [True, False, False]

 

A list can contain different data types:

 Example

A list with strings, integers and boolean values:

 list1 = ["abc", 34, True, 40, "male"]

type()

 From Python's perspective, lists are defined as objects with the data type 'list':

 <class 'list'>

Example

What is the data type of a list?

 

mylist = ["apple", "banana", "cherry"]

print(type(mylist))

 Output would be: <class 'list'>

 

 The list() Constructor

It is also possible to use the list() constructor when creating a new list.

 Example

Using the list() constructor to make a List:

 mylist = list(("Assam", "Benaras", "Chennai")) # note the double round-brackets