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S4 ICT: Python Dictionaries and File Handling (Paper 3 (challenge))
Tutor Prep Guide · Dictionary key lookup and the get default, membership tests, update and counting, reading a file line by line with strip, word frequency statistics, number conversion and averages, plus the mistakes students repeat most often
S4 ICT: Python Dictionaries and File Handling (Paper 3 (challenge))
Paper 3 (challenge): ten questions on Python dictionaries and file reading, with answers and notes.
Direct answers Level: S4 ICT; format: key lookup, get default, update and counting, line by line file reading, word frequency, number conversion.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 20 |
| Difficulty mix | Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1 |
| Chapter | Chapter: S4 ICT: Python Dictionaries and File Handling |
| Level | S4 |
02 Questions (10 items)
- FoundationIn {x: x * x for x in range(4)}, what is the value of key 3?
- FoundationWhat is the sum of all values in {x: x * x for x in range(5)}?
- FoundationHow many keys does {1: ‘a’, 1: ‘b’} have?
- Intermediatea = {‘x’: 1} and b = {‘x’: 9, ‘y’: 2}. After a.update(b), what are a[‘x’] and len(a)?
- IntermediateA data line Chan,85,Maths is split by comma; what integer do you get from the second field?
- IntermediateA file holds four lines 12, 7, 25 and 18. What is the difference between the largest and the smallest?
- ChallengeIn {‘A’: {‘math’: 80}, ‘B’: {‘math’: 95}}, what is B’s math score?
- ChallengeWhich word appears most often in red blue red green red?
- ChallengeWith counts = {‘red’: 3, ‘blue’: 1}, what is the first item of sorted(counts.items(), key=lambda kv: kv[1], reverse=True)?
- Error redoWhat happens if you add keys inside a for k in d loop?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 9 | The comprehension squares each key, and 3 squared is 9. |
| 2 | 30 | The values are 0, 1, 4, 9 and 16, which add to 30. |
| 3 | 1 | Keys are unique, so the second 1 overwrites the first and only 1 key remains, with value b. |
| 4 | 9 and 2 | update overwrites the shared key and adds the new one, so a[x] becomes 9 and the length is 2. |
| 5 | 85 | Indexing starts at 0, so the second field is 85, still 85 after int conversion. |
| 6 | 18 | The largest is 25 and the smallest 7, a difference of 18. |
| 7 | 95 | Two level indexing takes key B then key math, giving 95. |
| 8 | red | red appears three times while blue and green appear once each, so red wins. |
| 9 | (red, 3) | Sorting by value in descending order puts red with 3 first, returned as a key value pair. |
| 10 | It raises RuntimeError | Changing the size of a dictionary during iteration raises RuntimeError; iterate over a list copy instead. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
First ask where the data lives (a dictionary uses keys, a file uses lines), then choose len, get or a counting loop; strip the line ending after reading and convert strings to numbers before any arithmetic.Tutor Registration →
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