Quick Answer
The answer is FileNotFoundError, PermissionError, and IOError, as these are all direct subclasses of OSError in Python 3. This is because OSError serves as the base class for operating system-related exceptions, and its hierarchy organizes errors by specific failure types: FileNotFoundError triggers when a file or directory is missing, PermissionError occurs when access rights are denied, and IOError (now an alias for OSError itself) covers general input/output failures. On the Certified Associate Python Programmer PCAP exam, this tests your understanding of Python’s exception inheritance model, often appearing in multiple-choice questions that ask you to identify which exceptions belong to the OSError family. A common trap is confusing ValueError or TypeError as subclasses of OSError—they are not, as they derive from Exception directly. To remember, think of the acronym F-P-I: FileNotFound, Permission, and IO all fall under the OS umbrella.
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.
Which THREE of the following exception types are subclasses of OSError in Python 3?
FileNotFoundError
A subclass of OSError.
IOError
An alias for OSError, thus a subclass.
UnicodeError
Why wrong: Subclass of ValueError, not OSError.
PermissionError
A subclass of OSError.
EOFError
Why wrong: Subclass of Exception, not OSError.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
FileNotFoundError
FileNotFoundError is a direct subclass of OSError, raised when a file or directory is requested but does not exist at the given path. This is part of Python's exception hierarchy for operating system-related errors, specifically for file operations that fail due to missing resources.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
FileNotFoundError
Why this is correct
A subclass of OSError.
Related concept
Read the scenario before looking for a memorised answer.
IOError
Why this is correct
An alias for OSError, thus a subclass.
Related concept
Read the scenario before looking for a memorised answer.
UnicodeError
Why it's wrong here
Subclass of ValueError, not OSError.
PermissionError
Why this is correct
A subclass of OSError.
Related concept
Read the scenario before looking for a memorised answer.
EOFError
Why it's wrong here
Subclass of Exception, not OSError.
Common exam traps
Python Institute often tests the misconception that IOError is a separate exception type in Python 3, when in fact it is an alias for OSError, and that UnicodeError or EOFError belong to the OSError family, which they do not.
Detailed technical explanation
In Python 3, OSError is the base class for all system-related exceptions, and its subclasses include BlockingIOError, ChildProcessError, ConnectionError, FileExistsError, FileNotFoundError, InterruptedError, IsADirectoryError, NotADirectoryError, PermissionError, ProcessLookupError, and TimeoutError. IOError was merged into OSError in Python 3.0, so IOError is now an alias for OSError, making it technically a subclass. This hierarchy allows catching broad OS errors with a single except clause while still enabling fine-grained handling for specific conditions like missing files or permission denials.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
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FAQ
Exceptions and File I/O — This question tests Exceptions and File I/O — Read the scenario before looking for a memorised answer..
The correct answer is: FileNotFoundError — FileNotFoundError is a direct subclass of OSError, raised when a file or directory is requested but does not exist at the given path. This is part of Python's exception hierarchy for operating system-related errors, specifically for file operations that fail due to missing resources.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
This PCAP practice question is part of Courseiva's free Python Institute certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PCAP exam.
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