enumerate() function in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of enumerate with start index

What is the output of this Python code?

Python

items = ['apple', 'banana', 'cherry']
result = list(enumerate(items, start=1))
print(result)

A [(0, 'apple'), (1, 'banana'), (2, 'cherry')]

B [(1, 'apple'), (2, 'banana'), (3, 'cherry')]

C [(1, 'apple'), (1, 'banana'), (1, 'cherry')]

D [(0, 'apple'), (0, 'banana'), (0, 'cherry')]

💡 Hint

Remember that enumerate can start counting from any number you choose.

The enumerate function returns pairs of (index, item). The start=1 argument makes the index start at 1 instead of 0.

❓ Predict Output

intermediate

Using enumerate in a for loop

What will this code print?

Python

colors = ['red', 'green', 'blue']
for i, color in enumerate(colors):
    if i == 2:
        print(color)

A blue

B green

C red

D IndexError

💡 Hint

The loop prints the color when the index is 2.

The enumerate function pairs each color with its index starting at 0. When i is 2, the color is 'blue'.

🧠 Conceptual

advanced

Behavior of enumerate on empty iterable

What is the result of converting enumerate([]) to a list?

A [(1, None)]

B [(0, None)]

C []

D TypeError

💡 Hint

Think about what happens when you enumerate over an empty list.

Enumerate over an empty iterable produces no items, so converting to list results in an empty list.

❓ Predict Output

advanced

Output of enumerate with tuple unpacking

What does this code print?

Python

data = ['a', 'b', 'c']
for index, value in enumerate(data, 5):
    if index == 6:
        print(value)

A a

B IndexError

C c

D b

💡 Hint

The start index is 5, so the first item has index 5.

Enumerate starts counting at 5, so the second item has index 6, which is 'b'.

❓ Predict Output

expert

Effect of modifying list during enumerate

What happens when you run this code?

Python

lst = [10, 20, 30]
for i, val in enumerate(lst):
    if val == 20:
        lst.append(40)
print(len(lst))

A 4

B 3

C RuntimeError

D Infinite loop

💡 Hint

Think about how enumerate works with the list size changing during iteration.

Enumerate uses an iterator over the list. The list grows by one element during iteration, so the loop continues until the new element is processed. The final list length is 4.

Practice

1. What does the enumerate() function do in Python?

easy

A. It counts how many items are in a list.

B. It sorts the items in a list alphabetically.

C. It reverses the order of items in a list.

D. It returns both the index and the value of items in a list during a loop.

Solution

1. Step 1: Understand the purpose of enumerate()

   The enumerate() function adds a counter to an iterable and returns it as an enumerate object.

2. Step 2: Identify what is returned during looping

   When looping, it gives both the index (position) and the value of each item.

3. Final Answer:

   It returns both the index and the value of items in a list during a loop. -> Option D

4. Quick Check:

   enumerate() = index + value [OK]

Hint: Remember: enumerate() pairs index with value [OK]

Common Mistakes:

• Thinking enumerate() sorts the list
• Assuming it only counts items
• Believing it reverses the list

2. Which of the following is the correct syntax to use enumerate() in a for loop?

easy

A. for index in enumerate(list):

B. for value, index in enumerate(list):

C. for index, value in enumerate(list):

D. for value in enumerate(list):

Solution

1. Step 1: Recall the unpacking order of enumerate()

   enumerate() returns pairs of (index, value), so the loop variables must match this order.

2. Step 2: Match the correct variable order in the for loop

   The correct syntax is for index, value in enumerate(list): to unpack both index and value properly.

3. Final Answer:

   for index, value in enumerate(list): -> Option C

4. Quick Check:

   Index comes first, then value [OK]

Hint: Index always comes before value in enumerate() [OK]

Common Mistakes:

• Swapping index and value order
• Using only one variable to unpack both
• Forgetting to unpack both values

3. What is the output of this code?

fruits = ['apple', 'banana', 'cherry']
for i, fruit in enumerate(fruits, start=1):
    print(i, fruit)

medium

A. 1 apple
2 banana
3 cherry

B. 0 apple
1 banana
2 cherry

C. apple 0
banana 1
cherry 2

D. apple 1
banana 2
cherry 3

Solution

1. Step 1: Understand the start parameter in enumerate()

   The start=1 means counting begins at 1 instead of the default 0.

2. Step 2: Trace the loop output

   Loop prints index and fruit: 1 apple, 2 banana, 3 cherry.

3. Final Answer:

   1 apple 2 banana 3 cherry -> Option A

4. Quick Check:

   start=1 shifts index to 1 [OK]

Hint: Check start value to know index numbering [OK]

Common Mistakes:

• Assuming index starts at 0 despite start=1
• Mixing up index and value order in print
• Ignoring the start parameter

4. Find the error in this code snippet:

items = ['pen', 'pencil', 'eraser']
for value, index in enumerate(items):
    print(index, value)

medium

A. There is no error; the code runs fine.

B. The variables in the for loop are reversed; index should come first.

C. The print statement syntax is incorrect.

D. enumerate() cannot be used with lists.

Solution

1. Step 1: Check the order of variables unpacked from enumerate()

   enumerate() returns (index, value), so the first variable must be index.

2. Step 2: Identify the mistake in variable order

   The code uses value, index which is reversed and causes incorrect unpacking.

3. Final Answer:

   The variables in the for loop are reversed; index should come first. -> Option B

4. Quick Check:

   Index always first in enumerate() unpacking [OK]

Hint: Index comes before value in enumerate() unpacking [OK]

Common Mistakes:

• Swapping index and value variables
• Thinking enumerate() can't be used with lists
• Misreading the error as print syntax

5. You have a list of names: names = ['Anna', 'Bob', '', 'Diana']. You want to print only non-empty names with their positions starting at 1. Which code correctly does this using enumerate()?

hard

A. for i, name in enumerate(names, start=1):
if name:
print(i, name)

B. for i, name in enumerate(names):
if name != '':
print(i, name)

C. for i, name in enumerate(names, start=0):
if name:
print(i, name)

D. for i, name in enumerate(names, start=1):
if name == '':
print(i, name)

Solution

1. Step 1: Indexing starting at 1

   Use enumerate(names, start=1) to get positions starting from 1: 1 Anna, 2 Bob, 3 (empty), 4 Diana.

2. Step 2: Skip empty names

   Use if name: since empty string '' is falsy in Python.

3. Final Answer:

   for i, name in enumerate(names, start=1): if name: print(i, name) -> Option A

4. Quick Check:

   start=1 + if name skips empty [OK]

Hint: Use start=1 and if name to skip empty strings [OK]

Common Mistakes:

• Forgetting to start counting at 1
• Printing empty strings
• Not adjusting index when using default start=0