In this lesson we will:

1. Understand lists as mutable, ordered collections and learn to create, access, and modify them.
2. Perform basic operations on lists, including appending, removing, popping, slicing, sorting, and reversing.
3. Master iteration over lists using for loops to process data, such as calculating sums or displaying items.
4. Explore tuples as immutable alternatives to lists, including creation, access, and iteration.
5. Compare lists vs tuples to decide when to use each based on mutability, efficiency, and use cases like dictionary keys.
6. Apply these concepts in exercises, such as sorting lists, filtering even numbers, and calculating sums through coding tasks.

Lists are ordered collections of items that can be changed (mutable). They are defined using square brackets [] and can hold different data types, like numbers, strings, or even other lists. Lists are useful for storing multiple related items, such as a list of scores or names, and they allow you to organise data efficiently in your programs.

For example, fruits = ["apple", "banana", "cherry"] creates a list. You can access items by index, starting from 0, e.g., fruits[0] is "apple". Negative indices count from the end, so fruits[-1] is "cherry". Lists are dynamic, so you can add or remove items, and they can even be empty, like empty_list = [].

In the editor, add this complete code:

from microbit import *

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

display.scroll(fruits[0])

display.scroll(str(len(fruits)))

Lists are mutable, meaning you can change them after creation. Common operations include adding items with append(), removing specific values with remove(), or removing by index with pop() (which also returns the removed item). You can also slice lists to get sublists, similar to strings, e.g., list[1:3] extracts elements from index 1 to 2.

These operations help you manage and manipulate data dynamically in your programs.

Update your code to this complete version:

from microbit import *

numbers = [1, 2, 3]
numbers.append(4)
display.scroll(str(numbers))
numbers.remove(2)
display.scroll(str(numbers))
removed = numbers.pop(0)  # Removes and returns the first item
display.scroll("Removed: " + str(removed))
sliced = numbers[0:2]
display.scroll(str(sliced))

Iteration means going through each item in a list one by one, which is a powerful way to process data in collections. In Python, we often use a for loop for this purpose. A for loop allows you to execute a block of code repeatedly for each element in the list. This is especially useful for tasks like displaying all items, performing calculations on each one, or building summaries, such as calculating the sum or average of numbers in a list.

For example, if you have a list of scores, you can loop through them to show each score on the micro:bit display or add them up to find the total. Remember, the code inside the loop must be indented correctly (usually with four spaces) to indicate it belongs to the loop.

Update your code to this complete version:

from microbit import *

scores = [85, 92, 78, 90]
for score in scores:
    display.scroll(str(score) + " ")
total = 0
for score in scores:
    total += score
display.scroll("Total: " + str(total))

Sorting arranges list items in order. Use sort() for ascending order (modifies the list) or sorted() for a new sorted list. You can sort in descending order by passing reverse=True to these functions. Additionally, you can reverse the order of a list without sorting using the reverse() method, which modifies the list in place. These methods work both on numbers and strings.

Update your code to this complete version:

from microbit import *

numbers = [5, 3, 8, 1]
numbers.sort()
display.scroll(str(numbers))
numbers.reverse()
display.scroll(str(numbers))
fruits = ["cherry", "apple", "banana"]
sorted_fruits = sorted(fruits, reverse=True)
display.scroll(str(sorted_fruits))