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Software Engineering › Key terms › Code patterns › Python 2D list (grid)

Python 2D list (grid)

Code pattern Code patterns

Definition

A list of lists addressed as grid[row][column]; loop with nested for loops.

Example

grid[1][2] = 5

Found in: syllabus, course specifications, 2025 HSC marking guidelines, school notes, past SDD papers.

Where it is used in the test

Syllabus area: Code patterns.

Question types it can appear in

Where it has appeared in the paper

The Software Engineering Project (Part A, B). Part letters follow each paper’s own layout.

Related past questions

These are the questions the flashcard set links to this term. Open each one and compare your answer with its marking criteria.

Study links

How to use it in an answer

A model sentence

General advice, built from the definition and example above

Code pattern: “A list of lists addressed as grid[row][column]; loop with nested for loops.” Then apply it: grid[1][2] = 5

In a short answer, give the definition in your own words first, then tie it to the situation in the question. Do not copy the example above unless it fits the scenario.

Command words used with it

From the linked past questions
  • Identify: Recognise and name. (Sample exam Q21a (1 mark): 2D arrays (Python))

Technique for the question types

What the marking guidelines and feedback say

2025 HSC Q26 (5 marks): Design, construct and implement a solution (Python) · contains a reasoned or flagged note, read it as such

FLAG: the NESA sample tests pos (0 to 24) against numbers 1 to 25, so it is off by one (25 is never marked, 0 never appears). Safer: test pos + 1 in randList. Marker feedback: replicate the grid; use the random library; use selection and looping to access the list; include a method of checking the number of values; use meaningful variable names and constants; avoid overly complex structures such as nested IF loops.

Sample exam Q21b (5 marks): Python: subroutines, lists, loops

The key is the modulus: subjects[(period - day) % 5]. (The MG sample lists 'Art' where the question has 'Sport' - the program is meant to work with any five subjects.)

Worked answers from the marking guidelines

Sample exam Q21a (1 mark): 2D arrays (Python) (1 mark): criteria and sample answer

Criteria

1: Identifies the correct answer.

Sample answer

Timetable[0][2] (day index 0 = Monday, period index 2 = Period 3).

Open the question page

Sample exam Q21b (5 marks): Python: subroutines, lists, loops (5 marks): criteria and sample answer

Criteria

5: Substantially correct Python program that places each subject in the correct period; displays all 5 days; provides appropriate subroutines; programmatically builds the timetable. 4: Most requirements. 3: Some requirements. 2: One requirement. 1: Some understanding.

Sample answer

subjects = ["English", "Software", "Drama", "Science", "Art"] NUM_DAYS = 5 NUM_PERIODS = 5 DAYS_OF_WEEK = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"]

def create_timetable(subjects): timetable = [] for day in range(NUM_DAYS): periods = [] for period in range(NUM_PERIODS): periods.append(subjects[(period - day) % NUM_PERIODS]) timetable.append(periods) return timetable

def print_timetable(timetable): print() for day in range(NUM_DAYS): print(f"{DAYS_OF_WEEK[day]}") for period in range(NUM_PERIODS): print(f"\tPeriod {period+1}: {timetable[day][period]}") print()

timetable = create_timetable(subjects) print_timetable(timetable)

Open the question page

Common mistakes

Marker feedback on other questions of the same type (code and diagram feedback often applies across questions)
  • Python questions (2025 HSC exam Q19): process string inputs; use a selection structure; code must execute in the environment; use correct indentation; call functions in the main program after defining them.
  • Python questions (2025 HSC exam Q26): replicate the grid; use the random library; use selection and looping to access the list; include a method of checking the number of values; use meaningful variable names and constants; avoid overly complex structures such as nested IF loops.
General advice
  • Use the term exactly as the syllabus words it, then link it to the scenario in the question; the 2025 feedback repeatedly rewards using the stimulus.
  • Answer the command word: outline gives main points only, explain gives a reason or cause, discuss gives both sides.

Same group in the syllabus: Python input and output · Python selection (if elif else) · Python for loop and range · Python while loop · Python strings and slicing · Python lists · Python random numbers · Python functions · Global and local variables · Python file handling · Python modules and libraries · Python classes and objects · Python validation function pattern · Python try / except

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