Python Interview Question Bank — Data Engineer Edition
✅ Pro Tip
Quick-fire questions that interviewers ask to check your Python fundamentals. Each question includes multiple code examples, clear outputs, and interview tips.
Q01 — What is the difference between a list and a tuple?
Question: Explain the key differences between lists and tuples in Python. When would you use each?
Quick Answer: Lists are mutable (changeable), tuples are immutable (fixed). Tuples are faster, use less memory, and can be used as dictionary keys.
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# Example 1: Mutability difference
my_list = [1, 2, 3]
my_list[0] = 99 # Works fine — lists are mutable
print(my_list)
# Output: [99, 2, 3]
my_tuple = (1, 2, 3)
# my_tuple[0] = 99 # Raises: TypeError: 'tuple' object does not support item assignment
print(my_tuple)
# Output: (1, 2, 3)
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# Example 2: Tuples as dictionary keys (lists cannot do this)
# Tuples are hashable because they are immutable
coords = {(10, 20): "New York", (40, 50): "London"}
print(coords[(10, 20)])
# Output: New York
# Lists are NOT hashable — this would fail:
# bad_dict = {[10, 20]: "New York"}
# Raises: TypeError: unhashable type: 'list'
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120 bytes
print(f"Tuple size: {sys.getsizeof(my_tuple)} bytes")
# Output: Tuple size: 80 bytes
# Tuples use less memory because they don't need resize overhead"># Example 3: Memory and performance comparison
import sys
my_list = [1, 2, 3, 4, 5]
my_tuple = (1, 2, 3, 4, 5)
print(f"List size: {sys.getsizeof(my_list)} bytes")
# Output: List size: 120 bytes
print(f"Tuple size: {sys.getsizeof(my_tuple)} bytes")
# Output: Tuple size: 80 bytes
# Tuples use less memory because they don't need resize overhead🎯 Tip: "Tuples are hashable so they can be dict keys. Lists cannot because they're mutable. I use tuples for fixed data like DB row results or coordinates."
Q02 — What are Python's mutable and immutable types?
Question: Name Python's mutable and immutable types. What happens when you modify an immutable object?
Quick Answer: Immutable types (int, float, str, tuple, frozenset, bytes) create a new object on