Python Lists

What is a List?

A list is Python's most versatile data structure — an ordered, mutable collection that can hold any mix of types. "Ordered" means items stay in the position you put them. "Mutable" means you can add, remove, or change items after creation. Lists use square brackets [] and are one of the most frequently used structures in Python code.

fruits = ["apple", "banana", "cherry"]
mixed = ["hello", 42, True, 3.14]  # any types

print(fruits[0])    # first item
print(fruits[-1])   # last item
print(len(fruits))  # number of items

apple
cherry
3

Adding and Removing Items

append() adds to the end. insert(index, val) adds at a specific position. remove(val) deletes the first occurrence of a value (raises ValueError if not found). pop() removes and returns the last item (or a specific index if given) — useful when you need the removed value.

items = ["a", "b", "c"]
items.append("d")         # add to end
print(items)
items.insert(1, "x")      # insert at position 1
print(items)
items.remove("x")         # remove by value
print(items)
last = items.pop()         # remove and return last
print(f"Popped: {last} | Left: {items}")

['a', 'b', 'c', 'd']
['a', 'x', 'b', 'c', 'd']
['a', 'b', 'c', 'd']
Popped: d | Left: ['a', 'b', 'c']

Slicing

Slicing extracts a portion using list[start:stop:step] — same syntax as strings. The result is a new list; the original is unchanged. Leave start empty to begin from the start; leave stop empty to go to the end.

n = [0, 1, 2, 3, 4, 5, 6]
print(n[2:5])   # indices 2, 3, 4
print(n[:3])    # first 3
print(n[4:])    # from index 4 to end
print(n[::-1])  # reversed copy
print(n[::2])   # every 2nd item

[2, 3, 4]
[0, 1, 2]
[4, 5, 6]
[6, 5, 4, 3, 2, 1, 0]
[0, 2, 4, 6]

Sorting

list.sort() modifies the list in place. sorted(list) leaves the original untouched and returns a new sorted list. Both accept reverse=True for descending order.

nums = [3, 1, 4, 1, 5, 9]
nums.sort()
print(nums)

orig = [3, 1, 4]
s = sorted(orig)   # orig stays unchanged
print(orig, "→", s)

[1, 1, 3, 4, 5, 9]
[3, 1, 4] → [1, 3, 4]