Learning python - Tuples, Dictionaries and Sets

What is a tuple?

A tuple is a collection of items, similar to a list, but the key difference is that tuples cannot be changed. This means you cannot add, remove, or modify items once the tuple is created.

coordinates = (54.97, -1.60)

Tuples are useful when you want data to stay the same, such as settings, fixed information, or results loaded from a database.

How is a tuple different from a list?

A list is mutable (you can change it).
A tuple is immutable (you cannot change it).

numbers = [10, 20, 30]
numbers[1] = 99
# Result: [10, 99, 30]

Trying to change a tuple will cause an error:

fixed_numbers = (10, 20, 30)
# fixed_numbers[1] = 99  # Not allowed

Why use a tuple?

To protect data from being changed by accident
To improve speed in large programs (tuples are slightly faster than lists)
To store data that should stay constant

What is a dictionary?

A dictionary stores data in key–value pairs. The key is a label, and the value is the information connected to it. Keys can be numbers or strings and values can be any data type.

person = {
    "name": "Alice",
    "age": 30
}

Accessing values

print(person["name"])
# Output: Alice

Adding information to a dictionary

person = {"name": "Alice"}
person["city"] = "London"

This adds a new key–value pair.

Using `pop()`

pop() removes a key–value pair by its key. Useful when you want to delete information safely.

person.pop("city")

Using `update()`

update() adds or changes multiple key–value pairs at once.

person.update({"age": 31, "city": "London"})

Dictionaries inside dictionaries (nested dictionaries)

user = {
    "username": "alice01",
    "address": {
        "street": "North Road",
        "city": "Newcastle"
    }
}

Access inner values like this:

print(user["address"]["city"])

Looping through a dictionary with `items()`

items() gives you both the key and the value.

for key, value in person.items():
    print(key, value)

What is a set?

A set is a collection that automatically removes duplicate values.

scores = set([10, 10, 20, 30])
# Result: {10, 20, 30}

Sets are useful when

You want only unique items
You need fast membership checks

Storing a set in a variable

unique_names = {"Alice", "Bob", "Alice"}
# Result: {"Alice", "Bob"}

Common set methods

numbers = {1, 2, 3}
numbers.add(4)         # Add a value
numbers.discard(2)     # Remove a value
numbers2 = {3, 4, 5}

numbers.union(numbers2)        # Combine sets
numbers.intersection(numbers2) # Shared values
numbers.difference(numbers2)   # Values only in the first set

Summary

Tuples

Use brackets: ( )
Immutable (cannot change)
Best for fixed data

Dictionaries

Use { }
Key–value pairs
Can be nested

Sets

Use set()
No duplicates
Fast for comparisons

Vivienne Reay