Adding and updating key-value pairs in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add a new key-value pair to the dictionary.

Python

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

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

A'd'

B'b'

C'a'

D'c'

Attempts:

3 left

💡 Hint

Common Mistakes

Using an existing key will update the value, not add a new pair.

Forgetting to put the key in quotes if it is a string.

To add a new key-value pair, use a new key like 'c'.

2fill in blank

medium

Complete the code to update the value of an existing key in the dictionary.

Python

my_dict = {'x': 10, 'y': 20}
my_dict[[1]] = 30
print(my_dict)

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

A'z'

B'x'

C'a'

D'y'

Attempts:

3 left

💡 Hint

Common Mistakes

Using a new key will add a new pair instead of updating.

Forgetting to use quotes around the key string.

To update a value, use the existing key 'x'.

3fill in blank

hard

Fix the error in the code to add a key-value pair correctly.

Python

data = {'name': 'Alice'}
data[[1]] = 'Bob'
print(data)

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

A'age'

Bage

Cname

D'name'

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name without quotes causes a NameError.

Confusing keys with values.

Keys must be strings in quotes if they are text.

4fill in blank

hard

Fill both blanks to add a new key-value pair where the key is 'color' and the value is 'blue'.

Python

info = {'size': 'large'}
info[[1]] = [2]
print(info)

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

A'color'

B'blue'

C'red'

D'shape'

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping key and value positions.

Forgetting quotes around strings.

Use 'color' as the key and 'blue' as the value to add the pair.

5fill in blank

hard

Fill all three blanks to update the dictionary with a new key 'age' and value 25, then print the updated dictionary.

Python

person = {'name': 'John', 'city': 'NYC'}
person[[1]] = [2]
print([3])

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

A'age'

B25

Cperson

D'name'

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around numbers.

Printing a wrong variable name.

Use 'age' as the key, 25 as the value, and print the dictionary variable 'person'.

Practice

1. What happens when you use dictionary[key] = value in Python if the key already exists?

easy

A. A new key-value pair is added without changing the old one.

B. The value for that key is updated to the new value.

C. An error is raised because the key already exists.

D. The dictionary is cleared before adding the new pair.

Solution

1. Step 1: Understand dictionary key assignment

   Using dictionary[key] = value sets the value for the given key.

2. Step 2: Behavior when key exists

   If the key exists, the old value is replaced with the new one.

3. Final Answer:

   The value for that key is updated to the new value. -> Option B

4. Quick Check:

   Assigning existing key updates value [OK]

Hint: Assigning to existing key updates value, no error [OK]

Common Mistakes:

• Thinking it adds a duplicate key
• Expecting an error on existing key
• Assuming dictionary clears automatically

2. Which of the following is the correct syntax to add a new key-value pair 'color': 'blue' to a dictionary named car?

easy

A. car.color = 'blue'

B. car.add('color', 'blue')

C. car('color') = 'blue'

D. car['color'] = 'blue'

Solution

1. Step 1: Recall dictionary syntax for adding pairs

   Use dictionary[key] = value to add or update pairs.

2. Step 2: Check each option

   car['color'] = 'blue' uses correct syntax: car['color'] = 'blue'.

3. Final Answer:

   car['color'] = 'blue' -> Option D

4. Quick Check:

   Use square brackets for keys [OK]

Hint: Use square brackets and equals sign to add/update [OK]

Common Mistakes:

• Using parentheses instead of brackets
• Trying to call add() method which doesn't exist
• Using dot notation which works only for objects

3. What is the output of this code?

fruit_colors = {'apple': 'red', 'banana': 'yellow'}
fruit_colors['banana'] = 'green'
fruit_colors['cherry'] = 'red'
print(fruit_colors)

medium

A. {'apple': 'red', 'banana': 'yellow', 'cherry': 'red'}

B. {'apple': 'red', 'banana': 'green'}

C. {'apple': 'red', 'banana': 'green', 'cherry': 'red'}

D. SyntaxError

Solution

1. Step 1: Update existing key 'banana'

   The value for 'banana' changes from 'yellow' to 'green'.

2. Step 2: Add new key 'cherry'

   The pair 'cherry': 'red' is added to the dictionary.

3. Final Answer:

   {'apple': 'red', 'banana': 'green', 'cherry': 'red'} -> Option C

4. Quick Check:

   Update and add keys correctly [OK]

Hint: Updating key changes value; new key adds pair [OK]

Common Mistakes:

• Assuming old value stays after update
• Forgetting to add new key
• Expecting syntax error from valid code

4. Find the error in this code snippet:

data = {'x': 1, 'y': 2}
data['z'] == 3
print(data)

medium

A. Using '==' instead of '=' to add/update key-value pair.

B. Missing quotes around key 'z'.

C. Dictionary keys must be integers, not strings.

D. print() cannot display dictionaries.

Solution

1. Step 1: Identify the operator used for assignment

   The code uses '==' which is a comparison operator, not assignment.

2. Step 2: Correct operator for adding/updating dictionary

   Use '=' to assign value to a key in dictionary.

3. Final Answer:

   Using '==' instead of '=' to add/update key-value pair. -> Option A

4. Quick Check:

   Use '=' to assign values [OK]

Hint: Use single '=' to assign, not '==' [OK]

Common Mistakes:

• Confusing '==' with '='
• Thinking keys must be numbers
• Believing print can't show dictionaries

5. You have a dictionary inventory = {'apple': 5, 'banana': 3}. You want to add 2 more apples to the count. Which code correctly updates the inventory?

hard

A. All of the above

B. inventory['apple'] += 2

C. inventory.update({'apple': inventory['apple'] + 2})

D. inventory['apple'] = inventory['apple'] + 2

Solution

1. Step 1: Understand ways to update dictionary values

   You can update a value by direct assignment, augmented assignment, or using update() method.

2. Step 2: Check each option

   inventory['apple'] = inventory['apple'] + 2 adds 2 and assigns directly. inventory['apple'] += 2 uses += operator. inventory.update({'apple': inventory['apple'] + 2}) uses update() with new value.

3. Step 3: Confirm all methods work

   All three correctly increase 'apple' count by 2.

4. Final Answer:

   All of the above -> Option A

5. Quick Check:

   Multiple ways to update dictionary values [OK]

Hint: Multiple ways to update values, use any [OK]

Common Mistakes:

• Thinking only one method works
• Forgetting to add current value before assignment
• Using update() incorrectly without new value