Dictionary use cases in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of nested dictionary access

What is the output of this Python code?

Python

data = {'user': {'name': 'Alice', 'age': 30}, 'active': True}
print(data['user']['age'])

A 30

B 'Alice'

C True

D KeyError

💡 Hint

Look inside the nested dictionary under 'user' key.

The code accesses the 'user' dictionary inside 'data' and then gets the value for 'age', which is 30.

🧠 Conceptual

intermediate

Dictionary keys uniqueness

Which statement about Python dictionary keys is true?

A Dictionary keys can be duplicated if values differ.

B Dictionary keys must be unique and immutable.

C Dictionary keys can be mutable types like lists.

D Dictionary keys can be any data type including functions.

💡 Hint

Think about what happens if you try to use a list as a key.

Dictionary keys must be unique and immutable types like strings, numbers, or tuples. Mutable types like lists cannot be keys.

🔧 Debug

advanced

Identify the error in dictionary update

What error does this code raise?

Python

d = {'a': 1, 'b': 2}
d.update(['c', 3])

A No error, dictionary updated

B KeyError

C ValueError

D TypeError

💡 Hint

Check the argument type for update method.

The update method expects a mapping or iterable of key-value pairs. Passing a list of two elements causes a TypeError.

❓ Predict Output

advanced

Result of dictionary comprehension with condition

What is the output of this code?

Python

result = {x: x**2 for x in range(5) if x % 2 == 0}
print(result)

A {0: 0, 2: 4, 4: 16}

B {1: 1, 3: 9}

C SyntaxError

D {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}

💡 Hint

Only even numbers are included as keys.

The comprehension includes only keys where x is even, so keys 0, 2, and 4 with their squares as values.

🚀 Application

expert

Count character frequency in string using dictionary

What is the value of 'freq' after running this code?

Python

text = 'banana'
freq = {}
for ch in text:
    freq[ch] = freq.get(ch, 0) + 1
print(freq)

A {'b': 1, 'a': 3, 'n': 2}

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

C {'b': 1, 'a': 3, 'n': 3}

D KeyError

💡 Hint

Count how many times each letter appears in 'banana'.

The code counts each character's occurrences: 'b' once, 'a' three times, 'n' twice.