Adding and updating key-value pairs in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this dictionary update?

Consider the following Python code that updates a dictionary. What will be printed?

Python

data = {'a': 1, 'b': 2}
data['c'] = 3
data['a'] = 4
print(data)

A {'a': 1, 'b': 2}

B {'a': 1, 'b': 2, 'c': 3}

C {'a': 4, 'b': 2}

D {'a': 4, 'b': 2, 'c': 3}

💡 Hint

Remember that assigning a value to an existing key updates it.

The key 'c' is added with value 3, and the key 'a' is updated from 1 to 4.

❓ Predict Output

intermediate

What does this code print after using update()?

Look at this code snippet. What will be the output after the update method?

Python

info = {'name': 'Alice', 'age': 25}
info.update({'age': 30, 'city': 'NY'})
print(info)

A {'name': 'Alice', 'age': 30, 'city': 'NY'}

B {'name': 'Alice', 'age': 25, 'city': 'NY'}

C {'name': 'Alice', 'city': 'NY'}

D {'age': 30, 'city': 'NY'}

💡 Hint

The update method changes existing keys and adds new ones.

The 'age' key is updated to 30 and 'city' is added.

❓ Predict Output

advanced

What is the output when updating nested dictionaries?

What will this code print?

Python

settings = {'display': {'brightness': 70, 'contrast': 50}}
settings['display']['brightness'] = 80
settings['sound'] = {'volume': 40}
print(settings)

A {'display': {'brightness': 70, 'contrast': 50}, 'sound': {'volume': 40}}

B {'display': {'brightness': 80, 'contrast': 50}}

C {'display': {'brightness': 80, 'contrast': 50}, 'sound': {'volume': 40}}

D {'display': {'brightness': 70, 'contrast': 50}, 'sound': 40}

💡 Hint

Updating nested dictionary keys changes the inner dictionary values.

The brightness is updated to 80 inside 'display', and 'sound' is added as a new dictionary.

❓ Predict Output

advanced

What error does this code raise?

What error will this code produce?

Python

d = {'x': 1}
d[2,3] = 5
print(d)

A {'x': 1, (2, 3): 5}

B TypeError

C SyntaxError

D KeyError

💡 Hint

Can tuples be used as dictionary keys?

Tuples are immutable and can be dictionary keys, so no error occurs.

❓ Predict Output

expert

What is the final dictionary after these updates?

What will be printed after running this code?

Python

d = {'a': 1, 'b': 2}
updates = [('a', 3), ('c', 4), ('b', 5)]
for k, v in updates:
    d[k] = v
print(d)

A {'a': 1, 'b': 2, 'c': 4}

B {'a': 3, 'b': 5, 'c': 4}

C {'a': 3, 'b': 2, 'c': 4}

D {'a': 1, 'b': 5, 'c': 4}

💡 Hint

Each tuple updates or adds a key-value pair in the dictionary.

Keys 'a' and 'b' are updated to 3 and 5 respectively, 'c' is added with 4.