GCSE Python practice: debugging, algorithms and testing

The GCSE route in the TopMarks Code Lab gives direct access to 36 programming topics. Use it to repair a particular gap or practise applying an idea. There is no entry test and you do not need to finish the beginner route first. An optional recommendation activity can help you choose a starting point.

Choose a topic that matches the gap

• Programming foundations: variables, assignment, conversion, input, decisions, repetition, lists and functions.
• Control flow: selection, nested decisions, nested repetition and Boolean logic.
• Algorithms: linear and binary search, adjacent comparisons in bubble sort, and merging two sorted runs.
• Robust programs: debugging, range validation, expected results and test data.
• Applied practice: records, two-dimensional data, subroutines, constrained SQL tasks and a winning-team capstone.

Prerequisite links let you revisit an earlier idea and return to the task. If assignment or input conversion is the main difficulty, the beginner Python guide is a useful starting point.

Error Detective: test the rule, not just the example

Suppose a function must add two numbers and accept totals from 10 to 20 inclusive. This version runs, but it contains logic mistakes:

def is_success(num1, num2):
    total = num1 + num1
    return total > 10 and total < 20

Predict the result for unequal inputs and for totals exactly at both boundaries. An equal-input example can hide the repeated use of num1.

def is_success(num1, num2):
    total = num1 + num2
    return total >= 10 and total <= 20

Open Error Detective at the Prove stage to edit the program and run the supplied checks.

A useful 20-minute practice session

1. Predict: trace a short program and explain the expected result.
2. Explore: compare your trace with a replay or a real run.
3. Build: write or repair a small solution.
4. Check: inspect normal, boundary and erroneous cases where they fit the contract.
5. Apply: attempt a changed task and explain which part of the original idea transfers.

Write the expected result before running each test. ‘The program ran’ only tells you that execution reached the end; it does not prove that the rule is correct.

Know the scope of the resource

This is focused programming practice rather than a complete GCSE Computer Science specification. File handling and a full recursive merge-sort implementation are outside this release. SQL exercises use a clearly labelled simulator with fictional rows. The Python runner is a constrained subset with limits on execution, output, inputs and imports.

Use your school’s specification and official exam-board materials to check which additional topics you need. Practice checks are evidence about the current program, not a predicted exam grade. Saved drafts remain on this browser; download a copy for another device.

You can print this guide from your browser for lesson planning or independent study.