What Is List In Python

A list is a type of data structure in Python that is a mutable, or changeable, ordered sequence of elements.Each element or value that is inside of a list is termed as item. Just as strings are defined as characters between quotes, lists are defined by having values between square brackets [ ].

• In contrast with tuples, the length of lists is variable and their contents can be modified. They can be defined using square brackets [ ].

• Here, a list is defined using comma separated values of mixed data types.

• We can view the content of the list by just referring to the list object.

• You can use the append method to add a value to the list. Note that this value gets added to the end of the list.

• We can also remove any particular item by just referring to the element value.

• Use the pop method to simultaneously view and remove the value at a particular index.

• Similarly, use the insert method to insert a value at a particular index.

How To Print the elements of List In Python

CL = [100, 5.2, 'class', True]

print (CL)

Output:

[100, 5.2, 'class', True]

How To Update The Values In List In Python

To update the list elements you have to access first the element of the list by it's index value

List1 = ['physics', "chemistry", 1997, 2000]

print (List1)

print ()     

print ('Original Value at Index 2 = ', List1[2])          # access the value at index 2

List1[2] = "maths" # update 1997 to maths

print ()        

print ('Updated Value at Index 2 = ', List1[2])          # access the value at index 2

print ()

print ('Updated List = ', List1)

Output:

['physics', 'chemistry', 1997, 2000]

Original Value at Index 2 =  1997

Updated Value at Index 2 =  maths

Updated List =  ['physics', 'chemistry', 'maths', 2000]

How To Delete An Element Of List In Python 

List1 = ['physics', "chemistry", 1997, 2000]

print (List1)

print ()                                      #========================== Blank print

print ('Original Value at Index 2 = ', List1[2])          # access the value at index 2

del List1[2]

print ()

print ('Updated Value at Index 2 = ', List1[2]) # access the value at index 2

print ()

print ('Updated List = ', List1)

Output:

['physics', 'chemistry', 1997, 2000]

Original Value at Index 2 =  1997

Updated Value at Index 2 =  2000

Updated List =  ['physics', 'chemistry', 2000]

How To Access Elements From List In Python

list1 = ['physics', 'chemistry', 1997, 2000]

list2 = [1,2,3,4,5,6,7]

print (list1)

print ()

print (list2)

Output:

['physics', 'chemistry', 1997, 2000]

[1, 2, 3, 4, 5, 6, 7]

print (list1[0])

print (list2[1:5]) # [Start : Stop - 1]

Output:

physics

[2, 3, 4, 5]

How To Concatenate element values in List In Python

aList = [123, 'xyz', 'zara', 'abc']

bList = [2009, 'mani']

print (aList)

print (bList)

print ()

print (aList + bList)

print (bList + aList)

Output:

[123, 'xyz', 'zara', 'abc']

[2009, 'mani']

[123, 'xyz', 'zara', 'abc', 2009, 'mani']

[2009, 'mani', 123, 'xyz', 'zara', 'abc']

How To Do The Repetition Of The Elements In List In Python

aList = [123, 'xyz', 'zara', 'abc']

print (aList * 2)

Output:

[123, 'xyz', 'zara', 'abc', 123, 'xyz', 'zara', 'abc']

Different Inbuild Functions Of List In Python

# list append() -- Modify - adding a new value - appends an element to the end of the list

aList = [123, 'xyz', 'zara', 'abc']

print ('Original List : ', aList)

print ()

aList.append(2009)

print ('Updated List : ', aList)

Output:

Original List :  [123, 'xyz', 'zara', 'abc']

Updated List :  [123, 'xyz', 'zara', 'abc', 2009]

# Modify a list: Insert a new item at a certain index

aList = [123, 'xyz', 'zara', 'abc']

print ('Original List : ', aList)

print ()

aList.insert(2, 2009) # index and value --- insert 2009 at index 2

print ('Updated List : ', aList)

Output:

Original List :  [123, 'xyz', 'zara', 'abc']

Updated List :  [123, 'xyz', 2009, 'zara', 'abc']

# Remove - element -- Modifying the list
# remove deletes the item, does not display anything

aList = [123, 'xyz', 'zara', 'abc', 'xyz']

print ('List = ', aList)

print ()

aList.remove("xyz")

print ('List = ', aList)

print ()

aList.remove('zara')

print ('List = ', aList)

Output:

List =  [123, 'xyz', 'zara', 'abc', 'xyz']

List =  [123, 'zara', 'abc', 'xyz']

List =  [123, 'abc', 'xyz']

# pop() - The pop() method removes the item at the given index from the list and returns the removed item.

aList = [123, 'xyz', 'zara', 'abc']

print ('List = ', aList)

print ()

print (aList.pop(2)) # print the element or value which will be removed

print ()

print ('List = ', aList)

print ()

print (aList.pop()) # print the element or value which will be removed. when no indice is mentioned picks the last one

print ()

print ('List = ', aList)

Output:

List =  [123, 'xyz', 'zara', 'abc']

zara

List =  [123, 'xyz', 'abc']

abc

List =  [123, 'xyz']

#########How To Clear The List Elements

aList = [123, 'xyz', 'zara', 'abc']

print (aList)

print ()

# remove (aList)

aList.clear()  

print (aList) # empty list

del aList # now the list names aList doesn't exist

print (aList) # NameError: name 'aList' is not defined

Output:

[123, 'xyz', 'zara', 'abc']

[]

Error