Python Lists

Python Lists

Dealing with data in a structured format is quiet generous, and this is possible if those data are set accordingly in a specific manner. So, Python provides these data structures named ‘lists’ and ‘tuples’ that are used to organize data in  single set. Python has 6 built-in sequences and among them the most famous are “lists and tuples”.

The lists are containers that hold a number of other objects in a given order. It usually puts into practice the sequence protocol and allows programmers to add or remove objects from that sequence. Each element of the sequence is assigned a number i.e. he index and the first index is 0 (zero). This versatile data-type of Python is written in a sequence of list separated by commas between expressions.

Creating Lists

To build a list, just put a number of expressions in square brackets. The syntax is:

Syntax:

lst1 = [ ]  # lst1 is the name of the list
    lst2 = [expression1 , …. , expression_N]

Example:

#!/usr/bin/python

    lst1 = ['computersc', 'IT', 'CSE'];
    lst2 = [1993, 2016];
    lst3 = [2, 4, 6, "g", "k", "s"];

Accessing Lists Values

List apply the standard interface sequence in which len(L) returns the number of items present in the list and L[i] represents the item at index i. Also L[i:j] returns new list containing objects within ‘i’ and ‘j’.

Program to explain how to access lists:

Example:

#!/usr/bin/python

lst1 = ['computersc', 'IT', 'CSE'];
    lst2 = [1993, 2016];
    lst3 = [2, 4, 6, "g", "k", "s"];
    print "lst1[0]", lst1[0]
    print "lst3[2:4]", lst3[2:4]

Updating Lists

Program to show how to add/update single or multiple elements in a list:

Example:

#!/usr/bin/python

    lst1 = ['computersc', 'IT', 'CSE'];
    print " Second value of the list is:" 
    print lst1[1]

    lst1[1] = 'Robotics'
    print "Updated value in the second index of list is:"
    print lst1[1]

Delete Elements From Lists

To remove an element from list, we can use the del-statement. The syntax for deleting element from a list is:

Syntax:

del list_name[index_val];