The correct choice is the `__exit__` method that checks `if exc_type:` to conditionally call `rollback()` or `commit()`. This works because Python’s context manager protocol passes the exception type, value, and traceback into `__exit__`; when no exception occurs, `exc_type` is `None` (falsy), and when an exception is raised, `exc_type` is a class object (truthy). On the PCAP exam, this tests your understanding of the `with` statement’s lifecycle and how `__exit__` can handle cleanup logic differently based on success or failure. A common trap is forgetting that `exc_type` is `None` on normal exit, not `False`—so the idiomatic check is simply `if exc_type:` rather than comparing to `None`. For memory, think “rollback on raise, commit on clean”—the exception type acts as a flag for whether the block blew up.
PCAP Exceptions and File I/O Practice Question
This PCAP practice question tests your understanding of exceptions and file i/o. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A developer is implementing a custom context manager to manage database connections. The context manager should automatically roll back the transaction if an exception occurs, but commit if no exception occurs. Which pattern ensures this behavior correctly?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
def __exit__(self, exc_type, exc_val, exc_tb):
if exc_type:
self.connection.rollback()
else:
self.connection.commit()
Option B is correct because the `__exit__` method receives the exception type (`exc_type`), value (`exc_val`), and traceback (`exc_tb`) as arguments. By checking `if exc_type:` (which is `None` when no exception occurs, and a class object otherwise), the developer can conditionally roll back the transaction on an exception or commit if the block completes normally. This pattern ensures atomicity and proper resource management for database connections.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
Rolls back even if no exception, losing valid work.
✗
def __exit__(self, exc_type, exc_val, exc_tb):
if exc_val:
self.connection.rollback()
else:
self.connection.commit()
Why it's wrong here
exc_val can be None even if an exception occurred (if exception has no arguments), so not reliable.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Python Institute often tests the distinction between checking `exc_type` vs. `exc_val` vs. `exc_tb`, and candidates mistakenly think any of these three can be used interchangeably, but the canonical and most reliable check is `exc_type` because it is `None` when no exception occurs and a class object otherwise, while `exc_val` could theoretically be `None` even if an exception is raised (though rare).
Detailed technical explanation
How to think about this question
Under the hood, Python's `with` statement calls `__exit__` with three arguments: `None, None, None` if no exception occurs, or the exception type, value, and traceback if an exception is raised. The `exc_type` argument is a class (e.g., `<class 'ValueError'>`) when an exception occurs, which is truthy, while `None` is falsy. In real-world database drivers like `sqlite3` or `psycopg2`, failing to roll back on an exception can leave locks held or uncommitted writes, causing deadlocks or data corruption in concurrent environments.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Exceptions and File I/O — This question tests Exceptions and File I/O — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: def __exit__(self, exc_type, exc_val, exc_tb):
if exc_type:
self.connection.rollback()
else:
self.connection.commit() — Option B is correct because the `__exit__` method receives the exception type (`exc_type`), value (`exc_val`), and traceback (`exc_tb`) as arguments. By checking `if exc_type:` (which is `None` when no exception occurs, and a class object otherwise), the developer can conditionally roll back the transaction on an exception or commit if the block completes normally. This pattern ensures atomicity and proper resource management for database connections.
What should I do if I get this PCAP question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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