Python Nested Lists & Important Programs (Part 4)

A nested list is a list that contains one or more lists as its elements. Nested lists are useful for representing two-dimensional data such as marksheets, seating arrangements, matrices, and tables. This article also covers important CBSE practical programs based on lists.

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Learning Objectives

• Understand nested lists.
• Access nested list elements.
• Traverse nested lists using loops.
• Write important CBSE list programs.
• Apply list processing techniques.

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What is a Nested List?

A nested list is a list whose elements are themselves lists.

Example

marks=[
    [85,90,88],
    [78,81,75],
    [92,95,89]
]

Here, the outer list contains three inner lists.

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Accessing Nested List Elements

Use two indices to access an element:

marks=[
    [85,90,88],
    [78,81,75],
    [92,95,89]
]

print(marks[0][1])

print(marks[2][0])

Output

90
92

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Traversing a Nested List

marks=[
    [85,90],
    [78,81],
    [92,95]
]

for row in marks:
    for value in row:
        print(value,end=" ")
    print()

Output

85 90
78 81
92 95

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Program 1: Find the Maximum Value in a List

numbers=[12,45,78,23,56]

maximum=max(numbers)

print("Maximum =",maximum)

Output

Maximum = 78

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Program 2: Find the Minimum Value in a List

numbers=[12,45,78,23,56]

minimum=min(numbers)

print("Minimum =",minimum)

Output

Minimum = 12

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Program 3: Find the Mean (Average)

marks=[75,80,85,90,95]

mean=sum(marks)/len(marks)

print("Mean =",mean)

Output

Mean = 85.0

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Program 4: Linear Search

Linear search checks each element one by one until the required element is found.

numbers=[12,45,78,23,56]

key=int(input("Enter number to search: "))

found=False

for item in numbers:
    if item==key:
        found=True
        break

if found:
    print("Element Found")
else:
    print("Element Not Found")

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Program 5: Linear Search with Position

numbers=[12,45,78,23,56]

key=int(input("Enter number: "))

if key in numbers:
    print("Position =",numbers.index(key))
else:
    print("Not Found")

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Program 6: Count Frequency of an Element

numbers=[10,20,10,30,20,10]

key=int(input("Enter number: "))

print("Frequency =",numbers.count(key))

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Program 7: Count Frequency of All Elements

numbers=[10,20,10,30,20,10]

visited=[]

for item in numbers:
    if item not in visited:
        print(item,"=",numbers.count(item))
        visited.append(item)

Output

10 = 3
20 = 2
30 = 1

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Program 8: Find the Largest Number Without max()

numbers=[12,45,78,23,56]

largest=numbers[0]

for item in numbers:
    if item>largest:
        largest=item

print("Largest =",largest)

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Program 9: Find the Smallest Number Without min()

numbers=[12,45,78,23,56]

smallest=numbers[0]

for item in numbers:
    if item

Quick Revision



A nested list is a list inside another list.

Use two indices to access nested list elements.

max() returns the largest value.

min() returns the smallest value.

sum() and len() are used to calculate the mean.

Linear search checks elements one by one.

count() returns the frequency of an element.