Hackerrank Decorators and Closures

Question 1

What is a closure in Python?

Accepted Answer

A function that retains access to variables from its enclosing scope even after that scope has finished executing

Answer

A closure is an inner function that captures and remembers variables from its enclosing function's scope. The enclosing scope's variables persist as long as the closure exists, even after the outer function returns.

Question 2

What does the following code print?

python
def make_multiplier(n):
    def multiply(x):
        return x * n
    return multiply

double = make_multiplier(2)
print(double(5))

Accepted Answer

10

Answer

make_multiplier(2) returns the inner function multiply with n=2 captured in its closure. Calling double(5) executes multiply(5) with the remembered n=2, returning 5*2=10.

Question 3

What is the effect of applying a decorator using @syntax?

python
@my_decorator
def greet():
    return 'hello'

Accepted Answer

It is equivalent to greet = my_decorator(greet)

Answer

The @decorator syntax is syntactic sugar. @my_decorator above a function definition is exactly equivalent to writing greet = my_decorator(greet) immediately after the def block.

Question 4

Why is functools.wraps used inside a decorator?

Accepted Answer

To preserve the original function's __name__ and __doc__ on the wrapper function

Answer

Without @functools.wraps(func), the wrapper function replaces the original's metadata, making debugging harder. @functools.wraps(func) copies __name__, __doc__, and other attributes from the original function to the wrapper.

Question 5

What does the nonlocal keyword do in the following code?

python
def counter():
    count = 0
    def increment():
        nonlocal count
        count += 1
        return count
    return increment

Accepted Answer

Allows increment() to modify the count variable in counter()'s scope

Answer

Without nonlocal, count += 1 inside increment() would create a new local variable, causing an UnboundLocalError. nonlocal count tells Python to use the count from the nearest enclosing (non-global) scope — counter()'s frame.

(Hackerrank) HackerRank Python Certification Practice Test

(Hackerrank) HackerRank Python Certification Practice Test

Hackerrank Decorators and Closures