Class 10 Computer Science — Dictionaries and their keys

Look a value up in a dictionary by its key, and work out what adding a key or writing over one leaves behind.

Name: ________________________

1.A value is looked up by name rather than by position here. What does this program print?
```
prices = {"pen": 10, "book": 45, "bag": 90}
print(prices["book"])
```

2.Two values are looked up and added together. What does this program print?

weights = {"box": 25, "bag": 40, "cup": 5}
print(weights["box"] + weights["cup"])

3.A dictionary called counts holds {"pen": 4, "book": 9, "bag": 2, "map": 7, "cup": 6}. Match each piece of code to the number it gives.
- counts["book"]
- counts["map"]
- counts["pen"]
- counts["cup"]
- len(counts)
- 7
- 9
- 4
- 6
- 5
4.One of these two lines adds a pair and the other one does not. What does this program print?
```
stock = {"pen": 6}
stock["book"] = 3
stock["pen"] = 11
print(stock["pen"] + stock["book"])
```
5.A key the dictionary did not have is written to here. What does this program print?
```
stock = {"pen": 12, "book": 5}
stock["bag"] = 9
print(len(stock))
```
6.The dictionary is measured rather than looked in. What does this program print?
```
stock = {"red": 4, "blue": 7, "green": 2, "black": 9}
print(len(stock))
```
7.One line here both reads a value and writes one back under the same key. What does this program print?
```
totals = {"north": 30, "south": 12}
totals["south"] = totals["south"] + 8
print(totals["south"])
```
8.This line looks just like the last one, but the key it writes to is not new. What does this program print?
```
counts = {"red": 3, "blue": 8}
counts["red"] = 10
print(len(counts))
```

Answer key — Class 10 Computer Science — Dictionaries and their keys

1. 45
2. 30
3. counts["book"] → 9; counts["map"] → 7; counts["pen"] → 4; counts["cup"] → 6; len(counts) → 5
4. 14
5. 3
6. 4
7. 20
8. 2