Lists in Python

What is a List?

A list stores many values in one variable, in order, inside square brackets [ ]. Lists are mutable — you can add, remove and change items.

marks = [85, 92, 78, 90]
print(marks)
print(len(marks))   # how many items

Access & Slice

fruits = ["apple", "banana", "mango"]
print(fruits[0])     # first
print(fruits[-1])    # last
print(fruits[0:2])   # first two

List Methods

Program 1: Create & Loop Through

names = ["Aman", "Riya", "Karan"]
for name in names:
    print("Student:", name)

A for loop visits each item one by one — no index needed.

Program 2: Sum, Max and Min

marks = [85, 92, 78, 90, 88]
print("Total  :", sum(marks))
print("Highest:", max(marks))
print("Lowest :", min(marks))
print("Average:", sum(marks) / len(marks))

Built-in functions sum(), max(), min(), len() work directly on lists.

Program 3: Search in a List

numbers = [10, 25, 30, 45]
x = int(input("Search for: "))
if x in numbers:
    print(x, "found at position", numbers.index(x))
else:
    print(x, "not in list")

• x in numbers checks membership.
• .index(x) gives the position of the item.

Program 4: Sort & Remove Duplicates

data = [5, 2, 8, 2, 5, 1]
data = list(set(data))   # set removes duplicates
data.sort()              # then sort
print(data)

set(data) drops duplicates; list() turns it back; .sort() orders it.

List Comprehension (a peek)

A short way to build lists in one line:

squares = [x*x for x in range(1, 6)]
print(squares)

Common Mistakes

• Index out of range — marks[10] on a 4-item list errors.
• .remove(x) errors if x is not present.
• Confusing append (one item) with extend (many items).

Practice Tasks

1. Store 5 marks and print the total and average.
2. Find the largest number in a list without using max().
3. Count even and odd numbers in a list.
4. Remove duplicates from a list and sort it.

Summary

• Lists hold ordered, changeable items in [ ].
• Methods: append, insert, remove, pop, sort, reverse.
• sum/max/min/len work directly; in checks membership.