Python Interview Questions

Builtins, Control Flow & Scope Interview Questions

any()/all(), loop control flow, scope, closures, and Python's namespace model.

Question 1: What is a sentinel object?

Ans

A sentinel is a unique object used to represent a special state that cannot safely be confused with a normal value such as None.

Example

python
MISSING = object()
value = data.get("name", MISSING)
if value is MISSING:
    print("missing")

Important Point

Use identity comparison with the sentinel.

Question 2: What is truthiness?

Ans

Objects can be evaluated in Boolean contexts. False, None, numeric zero, empty strings, and empty containers are falsey by default; most other objects are truthy.

Example

python
items = []
if not items:
    print("empty")

Important Point

Custom classes can define `__bool__` or `__len__` to control truth testing.

Question 3: What is any()?

Ans

any() returns True when at least one item in an iterable is truthy and stops early once it finds one.

Example

python
values = [0, 0, 5, 0]
print(any(values))

Important Point

It short-circuits, so generators can avoid unnecessary work.

Question 4: What is all()?

Ans

all() returns True when every item in an iterable is truthy and stops at the first falsey item.

Example

python
values = [2, 4, 6]
print(all(x % 2 == 0 for x in values))

Important Point

`all([])` is True because there is no element that violates the condition.

Question 5: What is pass?

Ans

pass is a no-operation statement used where Python syntax requires a statement but no action is currently needed.

Example

python
class FutureFeature:
    pass

Important Point

`pass` does not mean 'skip the loop iteration'; use `continue` for that.

Question 6: pass vs continue vs break?

Ans

pass does nothing, continue skips to the next loop iteration, and break exits the loop.

Example

python
for n in range(5):
    if n == 1:
        continue
    if n == 4:
        break
    print(n)

Important Point

Use each based on control-flow intent; they are not interchangeable.

Question 7: What is else on a loop?

Ans

A loop's else block runs when the loop finishes normally without hitting break.

Example

python
for n in [1, 3, 5]:
    if n % 2 == 0:
        break
else:
    print("No even number")

Important Point

The loop else is tied to normal completion, not to whether the loop body executed at least once.

Question 8: What is sorted key function?

Ans

The key argument tells sorted() what value to compare for each element.

Example

python
names = ["Bob", "Alexander", "Amy"]
print(sorted(names, key=len))

Important Point

The key function is called to obtain comparison values; it does not need to return booleans.

Question 9: What is a namespace?

Ans

A namespace is a mapping from names to objects. Python has local, enclosing, global, and built-in namespaces, among others.

Example

python
x = 10
print(globals()["x"])

Important Point

Namespace concepts explain why two scopes can contain the same name without being the same binding.

Question 10: What is scope?

Ans

Scope defines where a name can be accessed directly. Python's name lookup follows local, enclosing, global, and built-in scopes.

Example

python
x = "global"
def f():
    x = "local"
    print(x)
f()

Important Point

A nested function can read an enclosing binding but needs `nonlocal` to reassign it.

Question 11: What is a closure cell?

Ans

When a nested function retains a variable from an enclosing scope, Python stores that captured binding in a closure cell accessible through function metadata.

Example

python
def outer():
    x = 10
    def inner(): return x
    return inner

f = outer()
print(f.__closure__)

Important Point

This is an implementation-level introspection detail; ordinary code should usually reason in terms of closures.

Question 12: What is function first-class object?

Ans

Python functions can be assigned to variables, stored in collections, passed as arguments, and returned from other functions.

Example

python
def greet(): return "Hello"
fn = greet
print(fn())

Important Point

This property enables callbacks, decorators, and higher-order functions.

Question 13: What is callable()?

Ans

callable() returns whether an object appears callable, meaning it can be invoked with parentheses according to Python's runtime rules.

Example

python
print(callable(len))
print(callable(10))

Important Point

Being callable does not guarantee that calling it with a particular argument list will succeed.

Question 14: What is the difference between None, False, and 0?

Ans

None represents absence of a value, False is a boolean false value, and 0 is the integer zero. They can all be falsey but have different types and meanings.

Example

python
print(None is None)
print(False == 0)
print(type(None), type(False), type(0))

Important Point

Do not use falsey checks when the requirement specifically distinguishes None from other falsey values.

Continue Your Preparation

Practice Coding ProblemsSolve problems in 5 languages Explore Java JobsLatest openings and internships Explore Java ProjectsBuild something for your resume Read Career BlogsInterview prep and career articles