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).

Question 33

Which of these is immutable?

Accepted Answer

frozenset. A frozenset can't be changed after creation, so it can be a dict key.

Question 34

What does the // operator do?

Accepted Answer

Floor division. 7 // 2 is 3; -7 // 2 is -4 (it rounds down).

Question 35

Which keyword skips the rest of the current loop iteration?

Accepted Answer

continue. break leaves the loop; pass does nothing.

Question 36

What is PEP 8?

Accepted Answer

Python's style guide. Naming, indentation and layout conventions.

Question 37

What does *args collect in a function definition?

Accepted Answer

Extra positional arguments as a tuple. **kwargs collects extra keyword arguments as a dict.

Question 38

What is a decorator?

Accepted Answer

A function that wraps another function to add behaviour. @decorator syntax applies it, e.g. @staticmethod.

Question 39

What is the difference between a list and a tuple?

Accepted Answer

Lists are mutable; tuples are immutable. Tuples are slightly faster and can be dict keys.

Question 40

Which module is used for regular expressions?

Accepted Answer

re. re.findall, re.sub, re.match.

Question 41

What does if __name__ == '__main__': check?

Accepted Answer

Whether the file is run directly rather than imported. Code under it doesn't run on import.

Question 42

What is the GIL in CPython?

Accepted Answer

A lock that lets only one thread run Python bytecode at a time. Use multiprocessing for CPU-bound parallelism.

Question 43

Which function converts '42' to the integer 42?

Accepted Answer

int(). int('42') returns 42.

Question 44

What does pip do?

Accepted Answer

Installs Python packages. pip install requests.

Question 45

What is a virtual environment (venv)?

Accepted Answer

An isolated set of installed packages for one project. Keeps project dependencies separate.

Question 46

Which is the correct way to open a file for appending?

Accepted Answer

open('f.txt', 'a'). 'w' overwrites; 'a' adds to the end.

Question 47

Which statement raises an exception on purpose?

Accepted Answer

raise. raise ValueError('bad input').

Question 48

What is self in a Python method?

Accepted Answer

The object the method is called on. Python passes it automatically.

Question 49

What does a @staticmethod not receive?

Accepted Answer

self or cls. It's a plain function inside the class namespace.

Question 50

What is duck typing?

Accepted Answer

Using an object based on its methods, not its declared type. 'If it walks like a duck and quacks like a duck…'

Question 51

What does this code print?
print([x * x for x in range(4)])

Accepted Answer

[0, 1, 4, 9]. Squares of 0 to 3.

Question 52

What does this code print?
print('hello'[::-1])

Accepted Answer

olleh. A step of -1 walks the string backwards.

Question 53

What does this code print?
print(-7 // 2)

Accepted Answer

-4. // rounds down (towards minus infinity).

Question 54

What does this code print?
print(-7 % 2)

Accepted Answer

1. In Python the remainder takes the sign of the divisor: -7 % 2 is 1.

Question 55

What does this code print?
a = [1, 2]
b = a
print(a is b)

Accepted Answer

True. Both names refer to the same list object.

Question 56

What does this code print?
a = [1, 2]
b = a
b.append(3)
print(a)

Accepted Answer

[1, 2, 3]. b and a are the same list, so appending through b changes a.

Question 57

What does this code print?
a = [1, 2]
b = a[:]
b.append(3)
print(a)

Accepted Answer

[1, 2]. a[:] makes a copy, so a is unchanged.

Question 58

What does this code print?
print({1, 2, 3, 3})

Accepted Answer

{1, 2, 3}. A set removes the duplicate 3.

Question 59

What does this code print?
print(len(max(['a', 'abc', 'ab'], key=len)))

Accepted Answer

3. max with key=len picks the longest word, 'abc'.

Question 60

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

Accepted Answer

a-b-c. join puts '-' between the items.

Question 61

What does this code print?
print('a,b,c'.split(','))

Accepted Answer

['a', 'b', 'c']. split(',') cuts at each comma.

Question 62

What does this code print?
print(sum(map(int, '123')))

Accepted Answer

6. sum of the list [1, 2, 3].

Question 63

What does this code print?
print(list(enumerate(['a', 'b'])))

Accepted Answer

[(0, 'a'), (1, 'b')]. enumerate pairs each item with its index.

Question 64

What does this code print?
print(dict(zip(['a', 'b'], [1, 2])))

Accepted Answer

{'a': 1, 'b': 2}. dict(zip(keys, values)) builds a dictionary.

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)?

Q33. Which of these is immutable?

Q34. What does the // operator do?

Q35. Which keyword skips the rest of the current loop iteration?

Q36. What is PEP 8?

Q37. What does *args collect in a function definition?

Q38. What is a decorator?

Q39. What is the difference between a list and a tuple?

Q40. Which module is used for regular expressions?

Q41. What does if __name__ == '__main__': check?

Q42. What is the GIL in CPython?

Q43. Which function converts '42' to the integer 42?

Q44. What does pip do?

Q45. What is a virtual environment (venv)?

Q46. Which is the correct way to open a file for appending?

Q47. Which statement raises an exception on purpose?

Q48. What is self in a Python method?

Q49. What does a @staticmethod not receive?

Q50. What is duck typing?

Q51. What does this code print?

Q52. What does this code print?

Q53. What does this code print?

Q54. What does this code print?

Q55. What does this code print?

Q56. What does this code print?

Q57. What does this code print?

Q58. What does this code print?

Q59. What does this code print?

Q60. What does this code print?

Q61. What does this code print?

Q62. What does this code print?

Q63. What does this code print?

Q64. What does this code print?

Q65. What does this code print?

Q66. What does this code print?

Q67. What does this code print?

Q68. What does this code print?

Q69. What does this code print?

Q70. What does this code print?

Q71. What does this code print?

Q72. What does this code print?

Q73. What does this code print?

Q74. What does this code print?

Q75. What does this code print?

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

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

Q41. What does if name == 'main': check?