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

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of zip with lists of different lengths

What is the output of this code?

list1 = [1, 2, 3, 4]
list2 = ['a', 'b']
result = list(zip(list1, list2))
print(result)

Python

list1 = [1, 2, 3, 4]
list2 = ['a', 'b']
result = list(zip(list1, list2))
print(result)

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

B [(1, 'a'), (2, 'b'), (3, None), (4, None)]

C [(1, 'a'), (2, 'b'), (3, ''), (4, '')]

D [(1, 'a'), (2, 'b'), (3, 'c'), (4, 'd')]

💡 Hint

zip stops when the shortest input is exhausted.

The zip function pairs elements from each list until one list runs out. Here, list2 has only 2 elements, so zip stops after pairing two elements.

❓ Predict Output

intermediate

Using zip with unpacking operator

What is the output of this code?

pairs = [(1, 'x'), (2, 'y'), (3, 'z')]
numbers, letters = zip(*pairs)
print(numbers)
print(letters)

Python

pairs = [(1, 'x'), (2, 'y'), (3, 'z')]
numbers, letters = zip(*pairs)
print(numbers)
print(letters)

A

(1, 2, 3)
('x', 'y', 'z')

B [(1, 2, 3), ('x', 'y', 'z')]

C [(1, 'x'), (2, 'y'), (3, 'z')]

D Error: cannot unpack

💡 Hint

The * operator unpacks the list of tuples into separate arguments for zip.

Using *pairs unpacks the list into separate tuples, so zip groups first elements together and second elements together, returning two tuples.

❓ Predict Output

advanced

Output of zip with generator expressions

What is the output of this code?

gen1 = (x*x for x in range(3))
gen2 = (x+1 for x in range(5))
result = list(zip(gen1, gen2))
print(result)

Python

gen1 = (x*x for x in range(3))
gen2 = (x+1 for x in range(5))
result = list(zip(gen1, gen2))
print(result)

A Error: generators cannot be zipped

B [(0, 1), (1, 2), (4, 3), (9, 4), (16, 5)]

C [(0, 1), (1, 2), (4, 3)]

D [(0, 1), (1, 2)]

💡 Hint

zip stops when the shortest generator is exhausted.

gen1 produces 3 values (0,1,4), gen2 produces 5 values (1,2,3,4,5). zip stops after 3 pairs because gen1 ends.

❓ Predict Output

advanced

Result of zipping dictionaries

What is the output of this code?

dict1 = {'a': 1, 'b': 2}
dict2 = {'x': 10, 'y': 20, 'z': 30}
result = list(zip(dict1, dict2))
print(result)

Python

dict1 = {'a': 1, 'b': 2}
dict2 = {'x': 10, 'y': 20, 'z': 30}
result = list(zip(dict1, dict2))
print(result)

A [('a', 1), ('b', 2), ('x', 10), ('y', 20), ('z', 30)]

B [('a', 'x'), ('b', 'y')]

C [('a', 'x'), ('b', 'y'), ('c', 'z')]

D Error: cannot zip dictionaries

💡 Hint

Iterating a dictionary yields its keys.

When you zip dictionaries, it zips their keys. dict1 has keys 'a' and 'b', dict2 has keys 'x', 'y', 'z'. zip stops after shortest dict keys.

🧠 Conceptual

expert

Behavior of zip with infinite iterator

Consider this code:

import itertools
infinite = itertools.count(1)
finite = [10, 20, 30]
result = list(zip(infinite, finite))
print(result)

What is the output?

A Error: cannot zip infinite iterator

B Infinite loop, program never ends

C [(1, 10), (2, 20), (3, 30), (4, None)]

D [(1, 10), (2, 20), (3, 30)]

💡 Hint

zip stops when the shortest input is exhausted, even if the other is infinite.

zip stops after the finite list ends. The infinite iterator produces values but zip stops after 3 pairs.

Practice

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

easy

A. Converts a string to uppercase

B. Sorts a list in ascending order

C. Removes duplicates from a list

D. Combines elements from multiple sequences into pairs or groups

Solution

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

   The zip() function takes multiple sequences and pairs their elements by position.

2. Step 2: Compare with other options

   Sorting, removing duplicates, and changing case are unrelated to zip().

3. Final Answer:

   Combines elements from multiple sequences into pairs or groups -> Option D

4. Quick Check:

   zip() pairs sequences [OK]

Hint: Remember: zip pairs elements from sequences together [OK]

Common Mistakes:

• Thinking zip sorts or filters data
• Confusing zip with string methods
• Assuming zip works on single sequences only

2. Which of the following is the correct syntax to use zip() with two lists a and b?

easy

A. zip(a, b)

B. zip[a, b]

C. zip a, b

D. zip(a + b)

Solution

1. Step 1: Recall the function call syntax

   Functions in Python are called with parentheses and arguments separated by commas, like zip(a, b).

2. Step 2: Check other options for syntax errors

   Using square brackets or missing parentheses causes syntax errors or incorrect calls.

3. Final Answer:

   zip(a, b) -> Option A

4. Quick Check:

   Function call uses parentheses [OK]

Hint: Use parentheses and commas to call functions [OK]

Common Mistakes:

• Using square brackets instead of parentheses
• Omitting parentheses
• Trying to add lists inside zip

3. What is the output of the following code?

list1 = [1, 2, 3]
list2 = ['a', 'b', 'c']
result = list(zip(list1, list2))
print(result)

medium

A. [(1, 'b'), (2, 'c'), (3, 'a')]

B. [(1, 2, 3), ('a', 'b', 'c')]

C. [(1, 'a'), (2, 'b'), (3, 'c')]

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

Solution

1. Step 1: Understand how zip() pairs elements

   It pairs elements by position: first with first, second with second, etc.

2. Step 2: Apply to given lists

   Pairs are (1, 'a'), (2, 'b'), (3, 'c').

3. Final Answer:

   [(1, 'a'), (2, 'b'), (3, 'c')] -> Option C

4. Quick Check:

   Pairs match positions [OK]

Hint: zip pairs elements by index until shortest list ends [OK]

Common Mistakes:

• Confusing zip with concatenation
• Mixing element order in pairs
• Expecting zip to combine all elements into one tuple

4. Identify the error in this code snippet:

list1 = [1, 2]
list2 = ['x', 'y', 'z']
for a, b, c in zip(list1, list2):
    print(a, b, c)

medium

A. zip() requires lists of the same length

B. Too many variables to unpack in the for loop

C. Missing parentheses in zip call

D. print statement syntax error

Solution

1. Step 1: Check the number of variables in the for loop

   The loop tries to unpack three variables (a, b, c) from each zipped tuple.

2. Step 2: Check what zip produces

   zip(list1, list2) produces tuples with 2 elements each, so unpacking 3 variables causes an error.

3. Final Answer:

   Too many variables to unpack in the for loop -> Option B

4. Quick Check:

   Unpack count must match tuple size [OK]

Hint: Unpack only as many variables as zipped sequences [OK]

Common Mistakes:

• Assuming zip requires equal length lists
• Forgetting zip returns tuples of length equal to input sequences count
• Ignoring Python unpacking rules

5. Given two lists:

names = ['Anna', 'Bob', 'Cathy', 'Dan']
scores = [85, 92, 78]

Which code correctly creates a dictionary pairing each name with their score, ignoring extra names?

hard

A. dict(zip(names, scores))

B. {names[i]: scores[i] for i in range(len(names))}

C. dict(zip(scores, names))

D. dict(zip(names + scores))

Solution

1. Step 1: Understand zip behavior with unequal lengths

   zip stops at the shortest list length, so extra names are ignored.

2. Step 2: Check dictionary creation

   Using dict(zip(names, scores)) pairs names with scores correctly.

3. Step 3: Analyze other options

   {names[i]: scores[i] for i in range(len(names))} causes IndexError (longer names list). dict(zip(scores, names)) reverses keys and values. dict(zip(names + scores)) is invalid syntax.

4. Final Answer:

   dict(zip(names, scores)) -> Option A

5. Quick Check:

   zip stops at shortest list, dict pairs correctly [OK]

Hint: Use dict(zip(keys, values)) to pair lists safely [OK]

Common Mistakes:

• Assuming zip fills missing values
• Reversing keys and values in dict
• Using invalid syntax for zip