Nested loops

Putting one loop inside another runs the inner loop completely for every round of the outer loop. Two loops over ten items each give a hundred rounds. That is how you visit every cell of a grid or every pair of items.

Build grids as a list of rows: create an empty row list in the outer loop, fill it in the inner loop, then append the row to the result. To pair items without repeats, let the inner index start one past the outer index.

for row in range(2):
    for col in range(3):
        print(row, col)
# (0,0) (0,1) (0,2) (1,0) (1,1) (1,2)

Your task

Write multiplication_table(n) returning a list of n rows, where row i holds i * 1 up to i * n, so multiplication_table(3) is [[1, 2, 3], [2, 4, 6], [3, 6, 9]]. Then write pairs(items) returning every pair of items as tuples, each pair once, in order: pairs(["a", "b", "c"]) is [("a", "b"), ("a", "c"), ("b", "c")].

def multiplication_table(n):
    rows = []
    for i in range(1, n + 1):
        row = []
        for j in range(1, n + 1):
            row.append(i * j)
        rows.append(row)
    return rows


def pairs(items):
    result = []
    for i in range(len(items)):
        for j in range(i + 1, len(items)):
            result.append((items[i], items[j]))
    return result