What does Topic 6 cover and how is it assessed?

Topic 6 (Problem solving with programming) is assessed in the onscreen practical Paper 2, written in Python 3 using your own IDE. It covers developing, reading, refining and debugging code; the program constructs (sequence, selection, repetition, iteration); primitive and structured data types; string handling; input, output and CSV file handling; validation and authentication; the arithmetic, relational and logical operators; and subprograms with parameters and global and local variables. All tasks can be solved with the Programming Language Subset.

What is the Programming Language Subset (PLS)?

The PLS is a document Pearson publishes that lists exactly which Python 3 features may appear in the practical Paper 2. Every problem in the exam can be solved using only the functionality in the PLS, so learning it thoroughly means you know the full set of language features you might need, such as input/output, selection, loops, lists, string operations, file handling and defining functions.

How do you handle files in Python for Edexcel?

Open a file with open(filename, mode), where mode is 'r' to read, 'w' to write (replacing the file) or 'a' to append. Loop over a file's lines with a for loop, remembering each line is text (use int() or float() for numbers and strip() to remove the newline). For a CSV file, use line.strip().split(',') to separate the comma-separated fields into a list. Always close the file with close().

What is the difference between a function and a procedure?

A function performs a task and returns a value using return, so its result can be used in an expression. A procedure performs a task but does not return a value; it is called for its effect, such as printing. Both may take parameters (values passed in). Edexcel states functions must return values and procedures do not.

How should I revise Topic 6 for Paper 2?

Program in Python regularly rather than only reading, because Paper 2 is practical. Drill input/output and conversion, selection and loops, lists and 2D lists, string operations (length, indexing, slicing, case), reading and writing CSV files, validation (length, presence, range, pattern checks with re-prompting loops), authentication, and writing functions and procedures with parameters and return values. Practise reading, refining and debugging given code too.

EnglandComputer Science

Edexcel GCSE Computer Science Topic 6 Problem solving with programming: developing code, constructs, data types, strings, files, validation and subprograms in Python

A deep-dive Edexcel GCSE Computer Science guide to Topic 6 Problem solving with programming, the onscreen Python paper. Covers developing and debugging code, the program constructs, primitive and structured data types, string handling, input, output and CSV files, validation, authentication and subprograms.

Generated by Claude Opus 4.816 min readTopic 6Updated 2026-06-02

Reviewed by: AI editorial process; not yet individually human-reviewed

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What Topic 6 actually demands
Developing code and the constructs
Data, strings and files
Validation, authentication and subprograms
Check your knowledge

What Topic 6 actually demands

Problem solving with programming is the practical heart of the qualification, assessed in the onscreen Paper 2 in Python 3. You must be able to design, read, write, refine and debug programs that solve real problems, using the constructs, data types, string operations, file handling, validation, authentication, operators and subprograms in the Programming Language Subset. This is a doing skill, so it must be practised at the keyboard.

This guide ties together the seven dot-point pages for Topic 6.

Developing code and the constructs

Good development uses decomposition and abstraction, converts an algorithm into code, and writes readable code (layout, indentation, comments, meaningful identifiers, white space). The three error types are syntax (will not run), logic (wrong result) and runtime (crashes), found by tracing and testing. The constructs are sequence, selection (if/elif/else), repetition (for for a known count, while for a condition) and iteration over a structure, with single entry and exit points.

Data, strings and files

The primitive types are integer, real, Boolean and char; the structured types are string, array (a list, in one or two dimensions) and record. Use variables for changing values and constants for fixed ones. String handling covers length (len), position (indexing from 0), substrings (slicing s[start:end]) and case conversion (upper, lower). Input is read with input() (always text, so convert), and CSV files are read and written with open(), looping over lines and using split(",").

Validation, authentication and subprograms

Validation checks input is sensible (length, presence, range and pattern checks), normally with a loop that re-prompts until the input is valid, to make programs robust. Authentication confirms identity by comparing an ID and password (a lookup) against stored values, granting access only if both match. Subprograms are functions (return a value) and procedures (do not), with parameters; programs also use the arithmetic, relational and logical operators, and local variables (inside a subprogram) versus global variables (anywhere).

Check your knowledge

A mix of recall and short coding questions covering Topic 6. Attempt them, then check against the solutions.

State the three types of program error. (1 mark)
State what input() returns in Python. (1 mark)
State the value of 17 % 5. (1 mark)
State what "computer"[0:3] returns. (1 mark)
State which file mode replaces a file's contents. (1 mark)
Name the validation check that confirms a field is not blank. (1 mark)
State the difference between a function and a procedure. (1 mark)
State where a local variable can be used. (1 mark)

Sources & how we know this

Pearson Edexcel GCSE (9-1) Computer Science (1CP2) specification — Pearson (2020)
Pearson Edexcel GCSE Computer Science Programming Language Subset (Python) — Pearson (2020)