Lists

What it means

A list is Python’s general-purpose, ordered, mutable sequence — [1, 2, 3]. You can add, remove, and change items after creation, access elements by index, and slice out sub-ranges. Lists are the default choice for “a bunch of things in order” unless you specifically need immutability (tuple) or uniqueness (set).

Examples

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

fruits.append("date")          # add to the end: ['apple', 'banana', 'cherry', 'date']
fruits.insert(1, "avocado")    # insert at index 1
fruits.remove("banana")        # remove by value
first_two = fruits[:2]         # slicing: ['apple', 'avocado']
fruits.sort()                  # sort in place

numbers = [n * n for n in range(5)]   # list comprehension: [0, 1, 4, 9, 16]

Common mistake

Using list.append() when you meant list.extend() — append adds its argument as a single element, even if that argument is itself a list.

combined = [1, 2, 3]
combined.append([4, 5])   # [1, 2, 3, [4, 5]]  <- nested list, probably not intended

combined = [1, 2, 3]
combined.extend([4, 5])   # [1, 2, 3, 4, 5]    <- correct, flattens the items in

Quick practice

What’s the difference between list.append(x) and list.extend(x)?

Answer
append adds x as a single new element (even if it's a list); extend adds each item from x individually.
What does my_list[-1] return?

Answer
The last element of the list — negative indices count from the end.
Is a list comprehension faster than building a list with a for loop and repeated .append() calls?

Answer
Yes, generally — comprehensions avoid the repeated attribute lookup and function-call overhead of .append(), and CPython optimizes them internally.