Log In Sign Up

Dictionaries and Sets: Efficient Data Retrieval #

Welcome back to our programming tutorial series! Today, we’ll explore two powerful data structures in Python: dictionaries and sets. These structures allow you to store and retrieve data efficiently, especially when working with unique values or key-value pairs.

What Are Dictionaries? #

A dictionary is an unordered collection of key-value pairs, where each key is unique. You can use a dictionary to store related pieces of information and access them using the corresponding key.

Creating Dictionaries: #

1# Empty dictionary
2my_dict = {}
3
4# Dictionary with key-value pairs
5person = {
6    "name": "Alice",
7    "age": 30,
8    "city": "New York"
9}

You can access dictionary values by referring to their keys:

1print(person["name"])  # Outputs: Alice
2print(person["age"])  # Outputs: 30

Adding, Updating, and Removing Dictionary Entries #

You can add new key-value pairs or update existing ones in a dictionary:

 1# Adding a new entry
 2person["job"] = "Engineer"
 3
 4# Updating an existing entry
 5person["age"] = 31
 6
 7# Removing an entry
 8del person["city"]
 9
10print(person)  # Outputs: {'name': 'Alice', 'age': 31, 'job': 'Engineer'}

Dictionary Methods #

Python provides several built-in methods to work with dictionaries:

 1# Get all keys
 2print(person.keys())  # Outputs: dict_keys(['name', 'age', 'job'])
 3
 4# Get all values
 5print(person.values())  # Outputs: dict_values(['Alice', 31, 'Engineer'])
 6
 7# Get key-value pairs
 8print(person.items())  # Outputs: dict_items([('name', 'Alice'), ('age', 31), ('job', 'Engineer')])
 9
10# Check if a key exists
11if "name" in person:
12    print("Name is present in the dictionary.")

Nested Dictionaries #

Dictionaries can also contain other dictionaries, allowing you to store more complex data structures.

 1people = {
 2    "person1": {
 3        "name": "Alice",
 4        "age": 30
 5    },
 6    "person2": {
 7        "name": "Bob",
 8        "age": 25
 9    }
10}
11
12print(people["person1"]["name"])  # Outputs: Alice

What Are Sets? #

A set is an unordered collection of unique elements. Sets are useful when you want to store non-duplicate items or perform mathematical set operations like union, intersection, and difference.

Creating Sets: #

1# Empty set
2my_set = set()
3
4# Set with unique elements
5fruits = {"apple", "banana", "cherry", "apple"}
6print(fruits)  # Outputs: {'apple', 'banana', 'cherry'}

Set Operations #

Python sets support various operations for handling unique elements:

 1# Adding elements
 2fruits.add("orange")
 3
 4# Removing elements
 5fruits.remove("banana")
 6
 7# Set operations
 8set1 = {1, 2, 3}
 9set2 = {3, 4, 5}
10
11# Union (all unique elements from both sets)
12print(set1 | set2)  # Outputs: {1, 2, 3, 4, 5}
13
14# Intersection (common elements in both sets)
15print(set1 & set2)  # Outputs: {3}
16
17# Difference (elements in set1 but not in set2)
18print(set1 - set2)  # Outputs: {1, 2}

Practical Exercise: Phone Book Application #

Now that you understand dictionaries and sets, let’s create a simple phone book application using dictionaries:

  1. Write a program that allows the user to:
    • Add a new contact (name and phone number).
    • Search for a contact by name.
    • Remove a contact by name.
  2. Use a set to keep track of unique contact names.

Here’s a starter example:

 1phone_book = {}
 2
 3def add_contact(name, phone):
 4    if name in phone_book:
 5        print(f"{name} is already in the phone book.")
 6    else:
 7        phone_book[name] = phone
 8        print(f"Added {name}: {phone}")
 9
10def search_contact(name):
11    if name in phone_book:
12        print(f"{name}: {phone_book[name]}")
13    else:
14        print(f"{name} is not found in the phone book.")
15
16def remove_contact(name):
17    if name in phone_book:
18        del phone_book[name]
19        print(f"Removed {name}")
20    else:
21        print(f"{name} is not found in the phone book.")
22
23# Example usage
24add_contact("Alice", "123-456-7890")
25add_contact("Bob", "987-654-3210")
26search_contact("Alice")
27remove_contact("Bob")

What’s Next? #

You’ve just learned how to work with dictionaries and sets, essential tools for managing key-value pairs and unique collections of data. In the next post, we’ll dive into practical applications of these data structures to solve real-world problems.

Happy coding, and we’ll see you in the next lesson!