Data Structures

Lists

A list is a collection of items, which can be of different types. Lists are mutable, meaning that you can change the elements of a list after it has been created. Lists are created using square brackets [] and elements are separated by commas.

# Syntax
list_name = [item1, item2, ...]

# Example
fruits = ["apple", "banana", "cherry"]

In the example above, we define a list called fruits that contains three string elements.

Accessing Elements

You can access individual elements of a list using their index. The index of the first element is 0, the index of the second element is 1, and so on. You can also use negative indices to access elements from the end of the list.

# Syntax
element = list_name[index]

# Example
fruits = ["apple", "banana", "cherry"]
print(fruits[0])  # Output: apple
print(fruits[-1])  # Output: cherry

In the example above, we access the first and last elements of the fruits list using their indices.

Modifying Elements

You can modify the elements of a list by assigning new values to them using their indices.

# Syntax
list_name[index] = new_value

# Example
fruits = ["apple", "banana", "cherry"]
fruits[1] = "orange"
print(fruits)  # Output: ['apple', 'orange', 'cherry']

In the example above, we change the second element of the fruits list from "banana" to "orange".

Adding and Removing Elements

You can add new elements to a list using the append method, and remove elements using the remove method.

# Syntax
list_name.append(new_item)
list_name.remove(item)

# Example
fruits = ["apple", "banana", "cherry"]
fruits.append("orange")
print(fruits)  # Output: ['apple', 'banana', 'cherry', 'orange']
fruits.remove("banana")
print(fruits)  # Output: ['apple', 'cherry', 'orange']

In the example above, we add "orange" to the fruits list using the append method, and remove "banana" from the list using the remove method.

Tuples

A tuple is a collection of items, similar to a list. However, tuples are immutable, meaning that you cannot change the elements of a tuple after it has been created. Tuples are created using parentheses () and elements are separated by commas.

# Syntax
tuple_name = (item1, item2, ...)

# Example
colors = ("red", "green", "blue")

In the example above, we define a tuple called colors that contains three string elements.

Accessing Elements

You can access individual elements of a tuple using their index, similar to lists.

# Syntax
element = tuple_name[index]

# Example
colors = ("red", "green", "blue")
print(colors[0])  # Output: red
print(colors[-1])  # Output: blue

In the example above, we access the first and last elements of the colors tuple using their indices.

Modifying Elements

Since tuples are immutable, you cannot modify the elements of a tuple after it has been created.

# Example
colors = ("red", "green", "blue")
colors[1] = "yellow"  # TypeError: 'tuple' object does not support item assignment

In the example above, attempting to change the second element of the colors tuple results in a TypeError.

Dictionaries

A dictionary is a collection of key-value pairs. Each key is associated with a value, and you can use the key to access the corresponding value. Dictionaries are mutable and can contain elements of different types. Dictionaries are created using curly braces {} and key-value pairs are separated by commas.

# Syntax
dict_name = {key1: value1, key2: value2, ...}

# Example
person = {"name": "Alice", "age": 25, "city": "New York"}

In the example above, we define a dictionary called person that contains three key-value pairs.

Accessing Elements

You can access the value associated with a key in a dictionary using the key.

# Syntax
value = dict_name[key]

# Example
person = {"name": "Alice", "age": 25, "city": "New York"}
print(person["name"])  # Output: Alice
print(person["age"])  # Output: 25

In the example above, we access the values associated with the "name" and "age" keys in the person dictionary.

Modifying Elements

You can modify the value associated with a key in a dictionary by assigning a new value to it.

# Syntax
dict_name[key] = new_value

# Example
person = {"name": "Alice", "age": 25, "city": "New York"}
person["age"] = 26
print(person)  # Output: {'name': 'Alice', 'age': 26, 'city': 'New York'}

In the example above, we change the value associated with the "age" key in the person dictionary from 25 to 26.

Adding and Removing Elements

You can add new key-value pairs to a dictionary by assigning a value to a new key, and remove key-value pairs using the pop method.

# Syntax
dict_name[new_key] = new_value
dict_name.pop(key)

# Example
person = {"name": "Alice", "age": 25, "city": "New York"}

# Add a new key-value pair
person["email"] = "alice@example.com"
print(person)  # Output: {'name': 'Alice', 'age': 25, 'city': 'New York', 'email': 'alice@example.com'}

# Remove a key-value pair
person.pop("age")
print(person)  # Output: {'name': 'Alice', 'city': 'New York', 'email': 'alice@example.com'}

In the example above, we add an "email" key-value pair to the person dictionary, and then remove the "age" key-value pair using the pop method.

Sets

A set is an unordered collection of unique elements. Sets are mutable and can contain elements of different types. Sets are created using curly braces {} and elements are separated by commas.

# Syntax
set_name = {item1, item2, ...}

# Example
fruits = {"apple", "banana", "cherry"}

In the example above, we define a set called fruits that contains three string elements.

Adding and Removing Elements

You can add new elements to a set using the add method, and remove elements using the remove method.

# Syntax
set_name.add(new_item)
set_name.remove(item)

# Example
fruits = {"apple", "banana", "cherry"}
fruits.add("orange")
print(fruits)  # Output: {'apple', 'banana', 'cherry', 'orange'}

fruits.remove("banana")
print(fruits)  # Output: {'apple', 'cherry', 'orange'}

In the example above, we add "orange" to the fruits set using the add method, and remove "banana" from the set using the remove method.

Set Operations

You can perform various set operations such as union, intersection, and difference using built-in methods.

# Example
set1 = {1, 2, 3}
set2 = {3, 4, 5}

# Union
print(set1 | set2)  # Output: {1, 2, 3, 4, 5}

# Intersection
print(set1 & set2)  # Output: {3}

# Difference
print(set1 - set2)  # Output: {1, 2}

In the example above, we perform the union, intersection, and difference operations on two sets set1 and set2.

Exercises

Write a program to count the frequency of elements in a list.
Write a program to remove duplicates from a list.
Write a program to find the intersection of two lists.
Write a program to check if a set is a subset of another set.
Write a program to perform the symmetric difference of two sets.