Python 24-Day Course - Day 3: Lists

Day 3: Lists

Creating Lists and Indexing

A list is an ordered, mutable collection.

fruits = ["apple", "banana", "cherry"]
numbers = [1, 2, 3, 4, 5]
mixed = [1, "hello", True, 3.14]

print(fruits[0])    # apple
print(fruits[-1])   # cherry

Slicing

nums = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
print(nums[2:5])    # [2, 3, 4]
print(nums[:3])     # [0, 1, 2]
print(nums[7:])     # [7, 8, 9]
print(nums[::2])    # [0, 2, 4, 6, 8]
print(nums[::-1])   # [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]

Key Methods

Method	Description	Example
`append(x)`	Add to end	`lst.append(4)`
`insert(i, x)`	Insert at position	`lst.insert(0, "a")`
`remove(x)`	Remove by value	`lst.remove("a")`
`pop(i)`	Remove and return by index	`lst.pop(0)`
`sort()`	Sort	`lst.sort()`
`reverse()`	Reverse	`lst.reverse()`
`index(x)`	Find index of value	`lst.index("a")`
`count(x)`	Count occurrences	`lst.count(1)`

List Operations

a = [1, 2, 3]
b = [4, 5, 6]
print(a + b)        # [1, 2, 3, 4, 5, 6]
print(a * 2)        # [1, 2, 3, 1, 2, 3]
print(3 in a)       # True
print(len(a))       # 3

Today’s Exercises

Take 5 numbers as input, store them in a list, and calculate the average.
Create a new list with duplicate elements removed from the original list.
Write a program that extracts only the common elements from two lists.