Lists and tuples

A list is an ordered, changeable collection — the workhorse for "many of something." A tuple is its immutable cousin. Both connect directly to the data-structures fundamentals lesson: the shape you choose decides what's easy.

Lists: ordered and mutable

nums = [3, 1, 2]
nums[0]            # 3   (index from 0)
nums.append(4)     # [3, 1, 2, 4]
nums[0] = 9        # [9, 1, 2, 4]   (lists can change in place)
len(nums)          # 4
nums.sort()        # [1, 2, 4, 9]

Like strings, lists slice with [start:stop]. Unlike strings, they're mutable — methods like append, sort, and remove change the list itself. (Recall the reference-vs-value idea: two names for one list both see the change.)

Iterating

A for loop walks the items directly — no indexing needed:

for n in nums:
    print(n)

Need the index too? enumerate gives you both:

for i, n in enumerate(nums):
    print(i, n)

Tuples: ordered and immutable

A tuple is a fixed, unchangeable sequence, written with parentheses (or just commas):

point = (3, 4)
point[0]        # 3
# point[0] = 9  # TypeError — tuples can't be changed
x, y = point    # "unpacking": x = 3, y = 4

Reach for a tuple when the collection shouldn't change — coordinates, a fixed pair, a function returning several values. The immutability is a feature: it signals "this won't be modified."

Where to go next

Lists hold values by position. Next: dictionaries and sets — holding values by key, and tracking uniqueness.