The correct choice is to wrap the open() call in a try-except block that catches FileNotFoundError and calls send_404() in the except block. This is correct because FileNotFoundError is the specific exception Python raises when open() attempts to access a file that does not exist, and catching only this exception ensures the application returns a 404 Not Found response for missing files without swallowing unrelated exceptions like KeyboardInterrupt, which would break the requirement. On the Certified Associate Python Programmer PCAP exam, this tests your understanding of exception hierarchy—FileNotFoundError is a subclass of OSError, and the exam often includes traps where broad except clauses catch too much or where the wrong exception type is used. A common mistake is catching OSError or Exception, which would also catch system-level errors or interrupts; the exam expects you to target the exact exception. Memory tip: think “FileNotFoundError for file-not-found” and remember that 404 is the HTTP equivalent of Python’s FileNotFoundError—both mean “it’s not there.”
PCAP Exceptions and File I/O Practice Question
This PCAP practice question tests your understanding of exceptions and file i/o. Compare every option against the stated constraints before choosing — the best answer satisfies all requirements, not just the most obvious one. 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 small web application allows users to download files from a server. The code uses open() without any exception handling. When a user requests a non-existent file, the server crashes with a traceback and returns a 500 Internal Server Error to the client. The team needs to modify the code to handle this situation gracefully: if the file does not exist, the application should return a 404 Not Found response (by calling a function send_404()). The application should not catch unrelated exceptions like KeyboardInterrupt. Which modification is the most appropriate?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Wrap the open() call in a try-except block catching FileNotFoundError, and in the except block call send_404().
Option D is correct because it catches the specific exception raised when a file is not found (FileNotFoundError), which is a subclass of OSError. This allows the code to return a 404 response for missing files while not catching unrelated exceptions like KeyboardInterrupt, as required. The except block calls send_404() to handle the missing file gracefully without crashing the server.
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.
✗
Wrap the entire request handling in a try-except block catching Exception, and if any exception occurs, call send_500().
Why it's wrong here
Too broad; would mask programming errors and give wrong status code.
✗
Check if the file exists using os.path.exists before opening, and if not, call send_404().
Why it's wrong here
Race condition possible; not the most Pythonic approach.
✗
Wrap the open() call in a try-except block catching OSError, and in the except block call send_404().
Why it's wrong here
Catches more than needed; e.g., permission errors would incorrectly return 404.
✓
Wrap the open() call in a try-except block catching FileNotFoundError, and in the except block call send_404().
Why this is correct
Specifically handles the missing file case without catching unrelated errors.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Python Institute often tests the distinction between catching a specific exception (FileNotFoundError) versus its parent class (OSError), and the trap here is that candidates may choose the broader OSError (Option C) thinking it covers all file-related errors, but that would incorrectly handle permission or other OS errors as 404s.
Detailed technical explanation
How to think about this question
FileNotFoundError is a subclass of OSError introduced in Python 3.3, specifically raised when a file or directory is requested but does not exist. Using a specific exception type avoids masking unrelated OS errors, such as PermissionError or IsADirectoryError, which should result in a 500 error. In real-world web applications, precise exception handling is critical for security and debugging, as overly broad catches can hide bugs or leak sensitive information.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
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: Wrap the open() call in a try-except block catching FileNotFoundError, and in the except block call send_404(). — Option D is correct because it catches the specific exception raised when a file is not found (FileNotFoundError), which is a subclass of OSError. This allows the code to return a 404 response for missing files while not catching unrelated exceptions like KeyboardInterrupt, as required. The except block calls send_404() to handle the missing file gracefully without crashing the server.
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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