Dictionary keys, values, and items in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of dictionary keys() method

What is the output of this code snippet?

Python

my_dict = {'a': 1, 'b': 2, 'c': 3}
print(list(my_dict.keys()))

A ['a', 'b', 'c']

B ['1', '2', '3']

C ['a', 'b', 'c', 'd']

D dict_keys(['a', 'b', 'c'])

💡 Hint

The keys() method returns a view of the dictionary's keys. Converting it to a list shows the keys as a list.

The keys() method returns a view object showing the keys. Converting it to a list gives ['a', 'b', 'c']. Option A shows the view object itself, not a list.

❓ Predict Output

intermediate

Output of dictionary values() method

What will this code print?

Python

data = {'x': 10, 'y': 20}
vals = data.values()
print(sum(vals))

A 30

B ['10', '20']

C TypeError

D dict_values([10, 20])

💡 Hint

The values() method returns a view of values which can be summed directly.

The values() method returns a view of the dictionary's values. sum() can add these numbers directly, resulting in 30.

❓ Predict Output

advanced

Output of iterating dictionary items

What is the output of this code?

Python

d = {'one': 1, 'two': 2}
for k, v in d.items():
    print(f"{k}:{v}")

A 1\n2

B ('one', 1)\n('two', 2)

C one\ntwo

D one:1\ntwo:2

💡 Hint

items() returns key-value pairs which are unpacked in the loop.

The loop unpacks each key-value pair and prints them in the format key:value on separate lines.

❓ Predict Output

advanced

Length of dictionary keys view

What does this code print?

Python

my_dict = {1: 'a', 2: 'b', 3: 'c'}
keys_view = my_dict.keys()
print(len(keys_view))

A TypeError

B 3

C dict_keys([1, 2, 3])

D 0

💡 Hint

The keys view supports len() to get the number of keys.

The keys() method returns a view of keys which supports len(), returning the number of keys in the dictionary.

❓ Predict Output

expert

Output of modifying dictionary during iteration

What happens when this code runs?

Python

d = {'a': 1, 'b': 2, 'c': 3}
for k in d.keys():
    if k == 'b':
        d.pop(k)
print(d)

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

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

C RuntimeError: dictionary changed size during iteration

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

💡 Hint

Modifying a dictionary while iterating over its keys causes an error.

Python raises a RuntimeError if the dictionary size changes during iteration over keys or items.

Practice

1. Which method would you use to get all the keys from a Python dictionary my_dict?

easy

A. my_dict.values()

B. my_dict.get()

C. my_dict.items()

D. my_dict.keys()

Solution

1. Step 1: Understand dictionary methods

   The keys() method returns all keys in the dictionary.

2. Step 2: Match method to requirement

   Since we want all keys, my_dict.keys() is the correct method.

3. Final Answer:

   my_dict.keys() -> Option D

4. Quick Check:

   keys() = my_dict.keys() [OK]

Hint: Keys come from keys(), values from values(), pairs from items() [OK]

Common Mistakes:

• Confusing keys() with values()
• Using get() which retrieves a single value
• Using items() which returns key-value pairs

2. Which of the following is the correct syntax to get all values from a dictionary data?

easy

A. data.values()

B. data.get_values()

C. data.values

D. values(data)

Solution

1. Step 1: Recall method syntax

   Dictionary methods require parentheses to call them, so values() is correct.

2. Step 2: Check each option

   data.values misses parentheses, get_values() and values(data) are invalid.

3. Final Answer:

   data.values() -> Option A

4. Quick Check:

   values() needs parentheses [OK]

Hint: Always add () to call dictionary methods like values() [OK]

Common Mistakes:

• Forgetting parentheses after method name
• Using non-existent methods like get_values()
• Trying to call values() as a function with dictionary argument

3. What is the output of this code?

my_dict = {'a': 1, 'b': 2}
print(list(my_dict.items()))

medium

A. [('a', 1), ('b', 2)]

B. ['a', 'b']

C. [1, 2]

D. Error

Solution

1. Step 1: Understand items() method

   The items() method returns key-value pairs as tuples.

2. Step 2: Convert items to list

   Using list() converts these pairs into a list of tuples: [('a', 1), ('b', 2)].

3. Final Answer:

   [('a', 1), ('b', 2)] -> Option A

4. Quick Check:

   items() = list of (key, value) pairs [OK]

Hint: items() returns pairs; list() shows them as list of tuples [OK]

Common Mistakes:

• Thinking items() returns only keys or only values
• Expecting a dictionary instead of list of tuples
• Confusing items() with keys() or values()

4. Find the error in this code snippet:

my_dict = {'x': 10, 'y': 20}
for key, value in my_dict.keys():
    print(key, value)

medium

A. Syntax error in for loop

B. keys() returns only keys, cannot unpack into two variables

C. Missing parentheses after print

D. No error, code runs fine

Solution

1. Step 1: Check what keys() returns

   keys() returns only keys, so each item is a single value, not a pair.

2. Step 2: Understand unpacking in for loop

   The loop tries to unpack each key into two variables, causing an error.

3. Final Answer:

   keys() returns only keys, cannot unpack into two variables -> Option B

4. Quick Check:

   keys() = keys only, no pairs [OK]

Hint: keys() gives one value per item; items() gives pairs [OK]

Common Mistakes:

• Trying to unpack keys() into two variables
• Confusing keys() with items()
• Assuming keys() returns key-value pairs

5. You have a dictionary grades = {'Alice': 85, 'Bob': 92, 'Charlie': 78}. Which code snippet correctly prints each student's name and grade using dictionary methods?

hard

A. for name, grade in grades.values():
print(name, grade)

B. for name, grade in grades.keys():
print(name, grade)

C. for name, grade in grades.items():
print(name, grade)

D. for grade in grades.values():
print(grade)

Solution

1. Step 1: Identify method to get pairs

   items() returns key-value pairs, perfect for name and grade.

2. Step 2: Check each option

   for name, grade in grades.values(): print(name, grade) unpacks grades.values() (single values): error. for name, grade in grades.keys(): print(name, grade) unpacks grades.keys() (single keys): error. for grade in grades.values(): print(grade) prints only grades. for name, grade in grades.items(): print(name, grade) correctly unpacks grades.items() pairs.

3. Final Answer:

   for name, grade in grades.items(): print(name, grade) -> Option C

4. Quick Check:

   items() gives key-value pairs for easy unpacking [OK]

Hint: Use items() to loop over keys and values together [OK]

Common Mistakes:

• Using values() when keys and values needed
• Unpacking values() which are single values
• Using keys() without accessing values