Python Interview Questions and Answers

Question 1

Which of these is a mutable data type in Python?

Accepted Answer

list. Lists can be changed after creation; tuples, strings and ints cannot.

Question 2

What is the output of type(3 / 2) in Python 3?
print(type(3 / 2))

Accepted Answer

<class 'float'>. / always returns a float in Python 3; // is integer (floor) division.

Question 3

Which keyword is used to define a function in Python?

Accepted Answer

def. Functions are defined with def name(params):

Question 4

What does len({1, 2, 2, 3, 3, 3}) return?
print(len({1, 2, 2, 3, 3, 3}))

Accepted Answer

3. A set keeps only unique values: {1, 2, 3}.

Question 5

Which statement about Python tuples is true?

Accepted Answer

They are immutable. Tuples can't be changed after creation and are written with ( ).

Question 6

What is the correct way to start a single-line comment in Python?

Accepted Answer

#. Python comments start with #.

Question 7

What does this code print?
print([1, 2, 3] * 2)

Accepted Answer

[1, 2, 3, 1, 2, 3]. Multiplying a list repeats it.

Question 8

Which method adds an item to the end of a list?

Accepted Answer

append(). list.append(x) adds x at the end. Sets use add().

Question 9

What does this code print?
def f(a, b=2):
    return a * b

print(f(3))

Accepted Answer

6. The default argument b=2 is used, so 3 * 2 = 6.

Question 10

What is the output of bool('') and bool('0')?
print(bool(''), bool('0'))

Accepted Answer

False True. Empty strings are falsy; any non-empty string, even '0', is truthy.

Question 11

Which of these creates an empty dictionary?

Accepted Answer

{}. {} is an empty dict; an empty set must be written set().

Question 12

What does the 'is' operator check?

Accepted Answer

Whether two names refer to the same object. is compares identity; == compares values.

Question 13

What does this code print?
def add(x, items=[]):
    items.append(x)
    return items

print(add(1), add(2))

Accepted Answer

[1, 2] [1, 2]. The default list is created once and shared between calls, a classic Python trap. Use None as the default instead.

Question 14

What is a lambda in Python?

Accepted Answer

A small anonymous function written in one expression. lambda x: x * 2 creates a function without a name.

Question 15

What does this code print?
def f():
    try:
        return 1
    finally:
        return 2

print(f())

Accepted Answer

2. The return inside try runs, but finally always runs too, and a return in finally overrides it.

Question 16

Which built-in function returns both index and value while looping?

Accepted Answer

enumerate(). for i, value in enumerate(items):

Question 17

What does zip([1, 2, 3], ['a', 'b']) produce when converted to a list?
print(list(zip([1, 2, 3], ['a', 'b'])))

Accepted Answer

[(1, 'a'), (2, 'b')]. zip stops at the shortest input.

Question 18

What is the purpose of __init__ in a Python class?

Accepted Answer

It initialises a new object's attributes. __init__ runs automatically when an object is created.

Question 19

What does this code print?
x = 10
def change():
    x = 5
change()
print(x)

Accepted Answer

10. The function creates its own local x; the global x stays 10.

Question 20

Which keyword lets a function modify a variable defined at module level?

Accepted Answer

global. global x inside the function refers to the module-level x. nonlocal is for enclosing functions.

Question 21

What does a generator function use instead of return to produce values one at a time?

Accepted Answer

yield. yield pauses the function and hands back a value; it resumes on the next request.

Question 22

What does this code print?
print(['a', 'b', 'c'][-2:])

Accepted Answer

['b', 'c']. Negative indexes count from the end; [-2:] takes the last two items.

Question 23

Which of these is NOT a valid Python variable name?

Accepted Answer

2nd_place. Names can't start with a digit.

Question 24

What is the result of 2 ** 3 ** 2 in Python?
print(2 ** 3 ** 2)

Accepted Answer

512. ** is right-associative: 3 ** 2 = 9 first, then 2 ** 9 = 512.

Question 25

Which exception is raised by int('abc')?

Accepted Answer

ValueError. The type is right (a string) but the value can't be converted.

Question 26

What does the with statement do when opening a file?

Accepted Answer

Closes the file automatically when the block ends. with uses a context manager so the file is closed even if an error happens.

Question 27

What does this code print?
d = {'a': 1, 'b': 2}
d['b'] = 3
print(d)

Accepted Answer

{'a': 1, 'b': 3}. Keys are unique: assigning to an existing key replaces its value.

Question 28

What is the difference between a list and a tuple?

Accepted Answer

Lists are mutable, tuples are immutable. That immutability also makes tuples usable as dictionary keys.

Question 29

What does this code print?
s = 'python'
print(s.upper(), s[::-1])

Accepted Answer

PYTHON nohtyp. upper() returns a new uppercase string; [::-1] reverses the original lowercase one.

Question 30

What does PEP 8 describe?

Accepted Answer

The style guide for Python code. PEP 8 covers naming, indentation (4 spaces), line length and other style rules.

Question 31

What does this code print?
count = 0
for n in [2, 5, 8, 11, 14]:
    if n % 2 == 0:
        count += 1
print(count)

Accepted Answer

3. 2, 8 and 14 are even, so count is 3.

Question 32

Which data structure would you use for fast membership checks (x in collection)?

Accepted Answer

set. Sets (and dict keys) use hashing, so 'in' is O(1) on average; lists are O(n).

Python Interview Questions and Answers

Q1. Which of these is a mutable data type in Python?

Q2. What is the output of type(3 / 2) in Python 3?

Q3. Which keyword is used to define a function in Python?

Q4. What does len({1, 2, 2, 3, 3, 3}) return?

Q5. Which statement about Python tuples is true?

Q6. What is the correct way to start a single-line comment in Python?

Q7. What does this code print?

Q8. Which method adds an item to the end of a list?

Q9. What does this code print?

Q10. What is the output of bool('') and bool('0')?

Q11. Which of these creates an empty dictionary?

Q12. What does the 'is' operator check?

Q13. What does this code print?

Q14. What is a lambda in Python?

Q15. What does this code print?

Q16. Which built-in function returns both index and value while looping?

Q17. What does zip([1, 2, 3], ['a', 'b']) produce when converted to a list?

Q18. What is the purpose of init in a Python class?

Q19. What does this code print?

Q20. Which keyword lets a function modify a variable defined at module level?

Q21. What does a generator function use instead of return to produce values one at a time?

Q22. What does this code print?

Q23. Which of these is NOT a valid Python variable name?

Q24. What is the result of 2 3 2 in Python?

Q25. Which exception is raised by int('abc')?

Q26. What does the with statement do when opening a file?

Q27. What does this code print?

Q28. What is the difference between a list and a tuple?

Q29. What does this code print?

Q30. What does PEP 8 describe?

Q31. What does this code print?

Q32. Which data structure would you use for fast membership checks (x in collection)?

Python Interview Questions and Answers

Q1. Which of these is a mutable data type in Python?

Q2. What is the output of type(3 / 2) in Python 3?

Q3. Which keyword is used to define a function in Python?

Q4. What does len({1, 2, 2, 3, 3, 3}) return?

Q5. Which statement about Python tuples is true?

Q6. What is the correct way to start a single-line comment in Python?

Q7. What does this code print?

Q8. Which method adds an item to the end of a list?

Q9. What does this code print?

Q10. What is the output of bool('') and bool('0')?

Q11. Which of these creates an empty dictionary?

Q12. What does the 'is' operator check?

Q13. What does this code print?

Q14. What is a lambda in Python?

Q15. What does this code print?

Q16. Which built-in function returns both index and value while looping?

Q17. What does zip([1, 2, 3], ['a', 'b']) produce when converted to a list?

Q18. What is the purpose of __init__ in a Python class?

Q19. What does this code print?

Q20. Which keyword lets a function modify a variable defined at module level?

Q21. What does a generator function use instead of return to produce values one at a time?

Q22. What does this code print?

Q23. Which of these is NOT a valid Python variable name?

Q24. What is the result of 2 ** 3 ** 2 in Python?

Q25. Which exception is raised by int('abc')?

Q26. What does the with statement do when opening a file?

Q27. What does this code print?

Q28. What is the difference between a list and a tuple?

Q29. What does this code print?

Q30. What does PEP 8 describe?

Q31. What does this code print?

Q32. Which data structure would you use for fast membership checks (x in collection)?

Q18. What is the purpose of init in a Python class?

Q24. What is the result of 2 3 2 in Python?