Accessing elements from the List

M3-R5.1 · Chapter 5: Sequence Data Types · 8 min read

Accessing elements from the List: In order to access the list items refer to the index number. Use the index operator [ ] to access an item in a list. The index must be an integer. Nested lists are accessed using nested indexing.

The values stored in a list can be accessed using the slice operator ([ ] and [:]) with indexes.

Ø List-name [start: end] will give you elements between indices start to end-1.

Ø The first item in the list has the index zero (0)

>>> number[2]

>>> number[-1]

>>> number[-8]

>>> number[8]

IndexError: list index out of range

>>> number[5]=55 #Assigning a value at the specified index

>>> number

[12, 56, 87, 45, 23, 55, 56, 27]

Example: Accessing elements from list

List = ["Python", "With", "J.P.Mishra"]

print("Accessing a element from the list")

print(List[0])

print(List[2])

Add Elements to a Python List:

We use the append () method to add an element to the end of a Python list.

Example:

fruits = ['apple', 'banana', 'orange']

print('Original List:', fruits)

fruits. append('cherry') # using append method

print('Updated List:', fruits)

Change List Items : We can change the items of a list by assigning new values using the = operator.

Example:

colors = ['Red', 'Black', 'Green']

print('Original List:', colors)

colors[2] = 'Blue'

print('Updated List:', colors)

Remove an Item From a List : We can remove an item from a list using the remove() method.

Example:

numbers = [2,4,7,9]

numbers.remove(4) # remove 4 from the list

print(numbers)

Python List Length : We can use the built-in len() function to find the number of elements in a list.

Example:

cars = ['BMW', 'Mercedes', 'Tesla']

print('Total Elements: ', len(cars))

Iterating Through a List : We can use a for loop to iterate over the elements of a list.

Example:

fruits = ['apple', 'banana', 'orange']

for i in fruits:

print(i)

Traversing a LIST: Traversing means accessing and processing each element.

Method-1:

>>> day=list(input("Enter elements :"))

Enter elements : sunday

>>> for d in day:

print(d)

Examples:

List Traverse using While loop

L1=[10,21,30,41,50,61,70,81,90,101]

i=0

while(i<10):

print (L1[i],end=",")

i=i+1

List Traverse using For loop

L1=[10,21,30,41,50,61,70,81,90,101]

for i in L1:

print (i,end=",")

List Traverse using While loop and len() function

L1=[10,21,30,41,50,61,70,81,90,101]

i=0

while(i<len(L1)):

print (L1[i],end=",")

i=i+1

Traverse a list and print even number

L1=[10,21,30,41,50,61,70,81,90,101]

i=0

while(i<len(L1)):

print (L1[i],end=",")

i=i+2

Print the element of list along with their indecs

L1=["P","R","A","K","A","S","H"]

length=len(L1)

for i in range (length):

print ("At positive index",i,"element is",L1[i])

Find the sum of element in a list

L1=[10,20,30,40,50]

sum=0

i=0

while(i<len(L1)):

sum=sum+L1[i]

i=i+1

print ("sum of all element=",sum)

Program to display total and the average value of the elements in the list

L1=[10,20,30,40,50]

tot=0

i=0

while(i<len(L1)):

tot=tot+L1[i]

i=i+1

avg=tot/len(L1)

print ("Total of all element=",tot)

print ("Average of all element=",avg)

List Operators:

Ø Joining operator +

Ø Repetition operator *

Ø Slice operator [ : ]

Ø Comparison Operator <, <=, >, >=, ==, !=

Joining Operator: It joins two or more lists.

Example:

>>> L1=['a',56,7.8]

>>> L2=['b','&',6]

>>> L3=[67,'f','p']

>>> list=L1+L2+L3

>>> list

['a', 56, 7.8, 'b', '&', 6, 67, 'f', 'p']

CONCATENATION

# list1 is a list of the First Five odd integers

>>> list1=[1,3,5,7,9]

# list2 is a list of the First Five even integers

>>> list2=[2,4,6,8,10]

# Elements of list1 followed by list2

>>> list1+list2 OUTPUT: [1,3,5,7,9, 2,4,6,8,10]

Repetition Operator: It replicates a list specified number of times.

Example:

>>> L1*3 ['a', 56, 7.8, 'a', 56, 7.8, 'a', 56, 7.8]

>>> 3*L1

['a', 56, 7.8, 'a', 56, 7.8, 'a', 56, 7.8]

>>> list1=[“Hello”] # Element of list1 Repeated 5 Times >>> >>>list1 * 5

OUTPUT: [“ Hello”, “ Hello”, “Hello”, “Hello”, “Hello”]

MENBERSHIP

>>> list1[ “ Varun ”, “ Ravindra ”, “ Amrit ”]

>>> “Amrit” in list1 OUTPUT: True

>>> “Nitin” in list1 OUTPUT: False

Slice Operator:

Syntax:

List-name [start:end] will give you elements between indices start to end-1.

#Initializes a list list1

>>> list1=[ ”Varun”, ”Ravindra”, ”Amrit”, ”Nitin”, ”Rahul”, ”Prajwal” ]

>>> list1[2:4]

OUTPUT: [”Amrit”, ”Nitin”]

>>> num=[12,56,87,45,23,97,56,27]

>>> num[2:-2]

OUTPUT: [87, 45, 23, 97]

#PRACTICE MORE

>>> list1[ start: stop ] # items start through stop-1

>>> list1[ start: ] # items start through the rest of the array

>>> list1[: Stop] # items From the beginning Through stop-1

>>> list1[: ] # A Copy of the Whole list

>>> list1[-1 ] # last item in the list

>>> list1[-2: ] # last 2 item in the list

>>> list1[:-2 ] # Everything except the last 2 item in the list

>>> list1[ : :-1 ] # all item in the List in Reverse order

>>> list1[ 1 : :-1 ] # The first Two item in the List in Reverse order

>>> list1[ : -3:-1 ] # The Last Two item in the List in Reverse order

>>> list1[ -3: : -1 ] # Every Thing Except Last Two item in the List in Reverse order

Comparison Operators:

Compares two lists
Python internally compares individual elements of lists in lexicographical order.
It compares the each corresponding element must compare equal and two sequences must be of the same type.
For non-equal comparison as soon as it gets a result in terms of True/False, from corresponding elements’ comparison. If Corresponding elements are equal, it goes to the next element and so on, until it finds elements that differ.

Example:

>>>L1, L2 = [7, 6, 9], [7, 6, 9]

>>>L3 = [7, [6, 9] ]

For Equal Comparison:

Comparison	Result	Reason
>>>L1==L2	True	Corresponding elements have same value and same type
>>>L1==L3	False	Corresponding values are not same

For Non-equal comparison:

Comparison	Result	Reason
>>> L1>L2	False	All elements are equal
>>> L2>L3	TypeError: '>' not supported between instances of 'int' and 'list'	in L2, element at the index 1 is int type and in L3 element at the index 1 is list type
>>>[3,4,7,8]<[5,1]	True	3<5 is True
>>>[3,4,7,8]<[3,4,9,2]	True	First two elements are same so move to next element and 7<9 is True
>>>[3,4,7,8]<[3,4,9,11]	True	7<9 is True
>>>[3,4,7,8]<[3,4,7,5]	False	8<5 is False