Dictionary use cases in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a dictionary with keys 'a' and 'b' and values 1 and 2.

Python

my_dict = {'a': [1], 'b': 2}

Drag options to blanks, or click blank then click option'

A1

B'1'

C3

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string '1' instead of number 1

Using wrong number like 3 or 0

The value for key 'a' should be the number 1, not a string or other number.

2fill in blank

medium

Complete the code to access the value of key 'name' from the dictionary.

Python

person = {'name': 'Alice', 'age': 30}
print(person[1])

Drag options to blanks, or click blank then click option'

A['Name']

B['name']

C['age']

D['NAME']

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong key case

Using key 'age' instead of 'name'

To get the value of 'name', use the exact key 'name' with correct case.

3fill in blank

hard

Fix the error in the code to add a new key 'city' with value 'Paris' to the dictionary.

Python

data = {'country': 'France'}
data[1] = 'Paris'
print(data)

Drag options to blanks, or click blank then click option'

A('city')

B.append('city')

C['city']

D.add('city')

Attempts:

3 left

💡 Hint

Common Mistakes

Using append or add methods which are for lists or sets

Using parentheses instead of brackets

To add a new key-value pair, use square brackets with the new key and assign the value.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps numbers to their squares for numbers greater than 2.

Python

squares = {x: x[1]2 for x in range(1, 6) if x [2] 2}

Drag options to blanks, or click blank then click option'

A**

B>

C<

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' instead of '**' for squaring

Using '<' instead of '>' for filtering

Use '**' to square a number and '>' to filter numbers greater than 2.

5fill in blank

hard

Fill all three blanks to create a dictionary from a list of tuples, including only items with value greater than 10.

Python

items = [('apple', 5), ('banana', 15), ('cherry', 20)]
result = [1]: [2] for [3] in items if [2] > 10}

Drag options to blanks, or click blank then click option'

Afruit

Bcount

Cfruit, count

Ditem

Attempts:

3 left

💡 Hint

Common Mistakes

Using single variable instead of unpacking

Using wrong variable names

Not filtering values correctly

Use 'fruit' as key, 'count' as value, and unpack tuples with 'for fruit, count'.

Practice

1. What is the main purpose of a dictionary in Python?

easy

A. To store data as key-value pairs for quick access

B. To store data in a fixed order like a list

C. To perform mathematical calculations

D. To create a sequence of numbers

Solution

1. Step 1: Understand dictionary structure

   Dictionaries store data in pairs where each key maps to a value.

2. Step 2: Identify dictionary use case

   This structure allows fast lookup by key, unlike lists which use indexes.

3. Final Answer:

   To store data as key-value pairs for quick access -> Option A

4. Quick Check:

   Dictionaries = key-value pairs [OK]

Hint: Remember: dictionaries use keys to find values fast [OK]

Common Mistakes:

• Confusing dictionaries with lists or sets
• Thinking dictionaries keep order like lists
• Assuming dictionaries store only numbers

2. Which of the following is the correct way to add a new key-value pair to a dictionary my_dict?

easy

A. my_dict.append('key', 'value')

B. my_dict.add('key', 'value')

C. my_dict['key'] = 'value'

D. my_dict.insert('key', 'value')

Solution

1. Step 1: Recall dictionary syntax for adding items

   To add or update a key-value pair, use square brackets with the key and assign a value.

2. Step 2: Check each option

   Only my_dict['key'] = 'value' correctly adds or updates the dictionary.

3. Final Answer:

   my_dict['key'] = 'value' -> Option C

4. Quick Check:

   Use square brackets to add/update dict items [OK]

Hint: Use square brackets and assignment to add dict items [OK]

Common Mistakes:

• Using list methods like append or insert on dictionaries
• Trying to use a non-existent add() method
• Confusing dictionary syntax with list syntax

3. What will be the output of the following code?

my_dict = {'a': 1, 'b': 2}
my_dict['c'] = 3
print(my_dict)

medium

A. Error: Cannot add new key

B. {'a': 1, 'b': 2}

C. {'c': 3}

D. {'a': 1, 'b': 2, 'c': 3}

Solution

1. Step 1: Understand dictionary update

   Adding my_dict['c'] = 3 adds a new key 'c' with value 3.

2. Step 2: Print the updated dictionary

   Printing shows all keys and values including the new one.

3. Final Answer:

   {'a': 1, 'b': 2, 'c': 3} -> Option D

4. Quick Check:

   Adding key updates dict content [OK]

Hint: Adding key-value pairs updates dictionary instantly [OK]

Common Mistakes:

• Expecting original dict without new key
• Thinking print shows only last added key
• Assuming error when adding new keys

4. Find the error in this code snippet:

my_dict = {'x': 10, 'y': 20}
print(my_dict['z'])

medium

A. KeyError because 'z' is not in the dictionary

B. SyntaxError due to wrong brackets

C. TypeError because dictionary keys must be integers

D. No error, prints 0

Solution

1. Step 1: Check dictionary keys

   Keys are 'x' and 'y', but 'z' is not present.

2. Step 2: Accessing missing key causes error

   Trying to print my_dict['z'] raises a KeyError.

3. Final Answer:

   KeyError because 'z' is not in the dictionary -> Option A

4. Quick Check:

   Access missing key = KeyError [OK]

Hint: Accessing missing keys causes KeyError [OK]

Common Mistakes:

• Assuming missing keys return 0 or None
• Confusing KeyError with SyntaxError
• Trying to use wrong bracket types

5. Given a list of tuples representing student names and scores:

students = [('Alice', 85), ('Bob', 90), ('Alice', 95)]

Which code correctly creates a dictionary with the latest score for each student?

hard

A. scores = dict(students)
scores['Alice'] = 85

B. scores = {name: score for name, score in students}

C. scores = {}
for name, score in students:
if name not in scores:
scores[name] = score

D. scores = {name: max(score) for name, score in students}

Solution

1. Step 1: Understand dictionary comprehension behavior

   When keys repeat, the last value overwrites earlier ones.

2. Step 2: Check each option

   scores = {name: score for name, score in students} uses comprehension that keeps the last score for 'Alice' (95). scores = dict(students) scores['Alice'] = 85 wrongly resets 'Alice' score. scores = {} for name, score in students: if name not in scores: scores[name] = score keeps only first score. scores = {name: max(score) for name, score in students} is invalid syntax.

3. Final Answer:

   scores = {name: score for name, score in students} -> Option B

4. Quick Check:

   Dict comprehension overwrites duplicate keys [OK]

Hint: Dict comprehension keeps last value for duplicate keys [OK]

Common Mistakes:

• Assuming dict keeps first value for duplicates
• Using invalid syntax for max(score)
• Manually overwriting values incorrectly