Python list

In Python, a list is a collection of items that are stored in a specific order. It's a versatile data type because it can store any type of data, such as numbers, strings, or even other lists. Lists are mutable, meaning you can change their content after they are created.

Key Characteristics of Lists:

• Ordered: Lists maintain the order of items as they are inserted. Each item in a list has a specific position, known as its index, which helps to identify and access it.
• Mutable: You can modify lists by adding, removing, or changing items. This flexibility makes lists very powerful for storing and manipulating data.
• Allows Duplicates: Lists can contain duplicate values. Each item in a list is identified by its value and position, so duplicates are stored separately but can exist within the list.

Example:

# Creating a list
my_list = [1, 2, 3, 'apple', 'banana']

# Accessing elements
print(my_list[0])  # Output: 1

# Slicing
print(my_list[2:4])  # Output: [3, 'apple']

# Modifying elements
my_list[3] = 'orange'
print(my_list)  # Output: [1, 2, 3, 'orange', 'banana']

# Adding elements
my_list.append('grape')
print(my_list)  # Output: [1, 2, 3, 'orange', 'banana', 'grape']

# Removing elements
my_list.remove(2)
print(my_list)  # Output: [1, 3, 'orange', 'banana', 'grape']

Python Built-in Functions

Python provides several built-in functions that can be used with lists:

• len(): Returns the number of elements in a list.
• append(): Adds an element to the end of the list.
• insert(): Inserts an element at a specified position.
• remove(): Removes the first occurrence of a specified element.
• pop(): Removes and returns the element at the specified position.
• index(): Returns the index of the first occurrence of a specified value.
• count(): Returns the number of occurrences of a specified element.
• sort(): Sorts the list.
• reverse(): Reverses the order of the list.

Example:

# Using built-in functions with lists
numbers = [3, 1, 4, 1, 5, 9, 2, 6, 5]

# len()
length = len(numbers)
print("Length of the list:", length)  # Output: Length of the list: 9

# Adding an element
numbers.append(7)
print(numbers)  # Output: [3, 1, 4, 1, 5, 9, 2, 6, 5, 7]

# insert element 10 at 2nd position
numbers.insert(2, 10)
print(numbers)  # Output: [3, 1, 10, 4, 1, 5, 9, 2, 6, 5, 7]

# Removing an element
numbers.remove(5)
print(numbers)  # Output: [3, 1, 10, 4, 1, 9, 2, 6, 5, 7]

# Removing element at 2nd position
popped = numbers.pop(2)
print("Popped element:", popped)  # Output: Popped element: 10
print("Updated list:", numbers)   # Output: Updated list: [3, 1, 4, 1, 9, 2, 6, 5, 7]

# Returns the index of the first occurrence of a value 1
index = numbers.index(1)
print("Index of first occurrence of 1:", index)  # Output: Index of first occurrence of 1: 1

# Returns the number of occurrences of a 1
count = numbers.count(1)
print("Number of occurrences of 1:", count)  # Output: Number of occurrences of 1: 2

# Sorting
numbers.sort()
print(numbers)  # Output: [1, 1, 2, 3, 4, 5, 6, 7, 9]

# Reverse
numbers.reverse()
print("Reversed list:", numbers)  # Output: Reversed list: [9, 7, 6, 5, 4, 3, 2, 1, 1]