Processing 2D lists and records with loops

Exam programs often load a table of data and ask for totals, the highest value or a count. Nested loops visit every cell of a 2D list.

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Row totals with nested loops

The outer loop picks a row; the inner loop visits each column in that row. Reset the total at the start of each row.
# Points scored by 3 players (rows) in 4 rounds (columns)
points = [[4, 7, 2, 9],
[6, 3, 8, 5],
[7, 7, 1, 4]]
for row in range(len(points)):
total = 0
for col in range(len(points[row])):
total = total + points[row][col]
print("Player", row, "total", total)
Output:
Player 0 total 22
Player 1 total 22
Player 2 total 19

Column totals

Swap the loops: the outer loop picks a column and the inner loop goes down the rows.
points = [[4, 7, 2, 9], [6, 3, 8, 5], [7, 7, 1, 4]]
for col in range(4):
total = 0
for row in range(3):
total = total + points[row][col]
print("Round", col, "total", total)
Output:
Round 0 total 17
Round 1 total 17
Round 2 total 11
Round 3 total 18

Lists of records

A record holds related fields of different types. A list of records is like a table: one record per row, one field per column. Use the field's index: s[0] is the name and s[2] is the score.
# Each record: [name, form, score]
students = [["Ana", "10A", 64], ["Ben", "10B", 81], ["Cy", "10A", 77], ["Dee", "10B", 58]]
best = students[0]
for s in students:
if s[2] > best[2]:
best = s
print(best[0], best[2])
count = 0
for s in students:
if s[1] == "10A":
count = count + 1
print(count)
Output:
Ben 81
2

Changing a value

Use two indexes to change one field of one record:
students = [["Ana", "10A", 64], ["Ben", "10B", 81]]
students[1][2] = students[1][2] + 5
print(students[1])
Output: ['Ben', '10B', 86]
Replacing a whole row: students[0] = ["Ana", "10C", 70].
Worked example

Using the points table, find the total for round 2 (the third column).

  1. Column index 2 holds 2, 8 and 1.
  2. 2 + 8 + 1 = 11

Answer: 11

Key idea

Use nested loops for 2D lists: outer loop for rows and inner loop for columns (or the other way round for column totals). A list of records stores one record per row; pick a field with its index.

Quick check

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Extra practice

2 more questions

Try each one, then tap to check.

  1. points = [[4, 7, 2, 9], [6, 3, 8, 5], [7, 7, 1, 4]]. What is points[1][2]?

    Show the answer

    Answer: 8

    points[1] is [6, 3, 8, 5]; index 2 in it is 8.

  2. This program prints a total for each player. What total is printed for Player 1?
    points = [[5, 1, 6, 3],
    [2, 8, 4, 7],
    [9, 3, 5, 2]]
    for row in range(len(points)):
    total = 0
    for col in range(len(points[row])):
    total = total + points[row][col]
    print("Player", row, "total", total)

    Show the answer

    Answer: 21

    Row 1 is [2, 8, 4, 7]: 2 + 8 + 4 + 7 = 21.

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Sources and references

Checked by the GCSE-ready editorial team, 17 October 2026. Last updated 2 October 2026. Spotted a mistake? Tell us and we will fix it.

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