Removing dictionary entries in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output after removing a key?

Consider the dictionary d = {'a': 1, 'b': 2, 'c': 3}. What is the output after running d.pop('b') and then printing d?

Python

d = {'a': 1, 'b': 2, 'c': 3}
d.pop('b')
print(d)

A {'a': 1, 'c': 3}

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

C KeyError

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

💡 Hint

The pop method removes the key and returns its value.

The pop method removes the specified key from the dictionary and returns its value. After popping 'b', the dictionary no longer contains 'b'.

❓ Predict Output

intermediate

What happens when deleting a non-existent key?

Given d = {'x': 10, 'y': 20}, what happens when you run del d['z']?

Python

d = {'x': 10, 'y': 20}
del d['z']

A None

B {'x': 10, 'y': 20}

C KeyError

D SyntaxError

💡 Hint

Deleting a key that does not exist causes an error.

Using del on a key that is not in the dictionary raises a KeyError because the key cannot be found.

❓ Predict Output

advanced

What is the output after filtering dictionary entries?

What is the output of this code?

d = {'a': 1, 'b': 2, 'c': 3, 'd': 4}
d = {k: v for k, v in d.items() if v % 2 == 0}
print(d)

Python

d = {'a': 1, 'b': 2, 'c': 3, 'd': 4}
d = {k: v for k, v in d.items() if v % 2 == 0}
print(d)

A {'b': 2, 'd': 4}

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

C {'a': 1, 'b': 2, 'c': 3, 'd': 4}

D TypeError

💡 Hint

Only keep items where the value is even.

The dictionary comprehension keeps only items where the value is divisible by 2 (even numbers). So keys 'b' and 'd' remain.

❓ Predict Output

advanced

What is the output after using popitem()?

Given d = {'x': 1, 'y': 2, 'z': 3}, what does d.popitem() return and what is the dictionary afterwards?

Python

d = {'x': 1, 'y': 2, 'z': 3}
popped = d.popitem()
print(popped)
print(d)

A

('y', 2)
{'x': 1, 'z': 3}

B

('x', 1)
{'y': 2, 'z': 3}

C

KeyError
{'x': 1, 'y': 2, 'z': 3}

D

('z', 3)
{'x': 1, 'y': 2}

💡 Hint

popitem removes and returns the last inserted item in Python 3.7+.

In Python 3.7 and later, dictionaries keep insertion order. popitem removes the last inserted key-value pair, which is ('z', 3).

🧠 Conceptual

expert

Which option causes a runtime error when removing dictionary entries?

Which of the following code snippets will cause a runtime error when trying to remove entries from a dictionary?

A

d = {'a': 1, 'b': 2}
keys = list(d.keys())
for key in keys:
    del d[key]

B

d = {'a': 1, 'b': 2}
for key in d:
    del d[key]

C

d = {'a': 1, 'b': 2}
d.pop('a')

D

d = {'a': 1, 'b': 2}
d.pop('c', None)

💡 Hint

Modifying a dictionary while iterating over it can cause errors.

Deleting keys from a dictionary while iterating over it directly causes a RuntimeError due to dictionary size change during iteration.