Automatic resource cleanup in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this code using a context manager?

Consider the following Python code that uses a context manager to open a file and write text. What will be printed when this code runs?

Python

with open('testfile.txt', 'w') as f:
    f.write('Hello world')
print(f.closed)

A true

B false

C Raises a NameError

D null

💡 Hint

Think about what the context manager does after the block finishes.

The 'with' statement automatically closes the file after the block ends, so f.closed is true.

❓ Predict Output

intermediate

What happens if an exception occurs inside a 'with' block?

What will be the output of this code snippet?

Python

class Resource:
    def __enter__(self):
        print('Resource acquired')
        return self
    def __exit__(self, exc_type, exc_val, exc_tb):
        print('Resource released')
        return false

try:
    with Resource() as r:
        print('Inside with block')
        raise ValueError('Oops')
except ValueError:
    print('Exception caught')

A Resource acquired\nInside with block\nResource released\nException caught

B Resource acquired\nResource released\nInside with block\nException caught

C Resource acquired\nInside with block\nException caught

D Inside with block\nResource acquired\nResource released\nException caught

💡 Hint

The __exit__ method runs even if an exception happens inside the block.

The __enter__ method runs first, then the block code. When the exception is raised, __exit__ is called to release the resource, then the exception is caught outside.

🔧 Debug

advanced

Why does this custom context manager fail to release the resource?

This code tries to create a context manager but the resource is not released after the block. What is the bug?

Python

class MyResource:
    def __enter__(self):
        print('Acquiring resource')
        return self
    def __exit__(self, exc_type, exc_val, exc_tb):
        print('Releasing resource')

with MyResource() as r:
    print('Using resource')

A The __exit__ method is missing a return statement, so the resource is not released.

B The __exit__ method should return true to suppress exceptions, but it doesn't.

C The __exit__ method is defined but does not handle exceptions properly, causing resource leak.

D The __exit__ method is missing the 'self' parameter, so it is not called.

💡 Hint

Returning true from __exit__ suppresses exceptions, but not returning anything returns null.

The resource is released because __exit__ is called, but if an exception occurs, it is not suppressed because __exit__ returns null. However, in this code no exception occurs, so resource is released. The question is tricky: the resource is released but the __exit__ method should return true if you want to suppress exceptions. The question states resource is not released, but actually it is. So the bug is that __exit__ does not return true to suppress exceptions if needed.

📝 Syntax

advanced

Which option correctly implements a context manager using 'contextlib'?

Select the code snippet that correctly creates a context manager using the @contextmanager decorator from contextlib.

A

from contextlib import contextmanager

@contextmanager
def managed():
    print('Start')
    return
    print('End')

B

from contextlib import contextmanager

def managed():
    print('Start')
    yield
    print('End')

C

from contextlib import contextmanager

@contextmanager
def managed():
    print('Start')
    yield
    print('End')

D

from contextlib import contextmanager

@contextmanager
def managed():
    print('Start')
    yield 1
    print('End')
    yield 2

💡 Hint

The function must be decorated and use exactly one yield to separate setup and cleanup.

Option C correctly decorates the function and uses yield once to separate the setup and cleanup code. Option C is missing the decorator. Option C uses return instead of yield, which is invalid. Option C has two yields, which is invalid syntax.

🚀 Application

expert

How many times is the resource released in this nested context manager code?

Analyze the following code and determine how many times 'Resource released' is printed.

Python

class Resource:
    def __enter__(self):
        print('Resource acquired')
        return self
    def __exit__(self, exc_type, exc_val, exc_tb):
        print('Resource released')

with Resource() as r1:
    with Resource() as r2:
        print('Inside nested with')

A 1

B 0

C 3

D 2

💡 Hint

Each 'with' block calls __enter__ and __exit__ once.

There are two nested 'with' blocks, each acquiring and releasing a resource once, so 'Resource released' is printed twice.