PCAP Exceptions and File I/O Practice Test 3 — 15 Questions

Question 1

Match each Python module to its purpose.

Accepted Answer

os: Provides a portable way of using operating system dependent functionality.. Common Python standard library modules: os (operating system interface), sys (interpreter access), json (JSON handling), datetime (date and time), re (regular expressions), math (mathematical functions).

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os: Provides access to some variables used or maintained by the interpreter.

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sys: Provides functions for working with dates and times.

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json: Provides support for regular expressions.

Question 2

A developer writes a function that reads a file and processes its content. The function should handle the case where the file does not exist without catching other I/O errors. Which exception should be caught?

Accepted Answer

FileNotFoundError. `FileNotFoundError` is a specific subclass of `OSError` that is raised exactly when a file or directory is requested but does not exist. By catching only `FileNotFoundError`, the function handles the missing-file scenario without masking other I/O errors such as permission issues or disk failures, which is the precise requirement stated in the question.

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PermissionError

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IOError

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OSError

Question 3

A developer is writing a script that processes user-uploaded CSV files. The script should attempt to read the file, and if a UnicodeDecodeError occurs, log a warning and skip the file. Which code snippet correctly achieves this without stopping the entire process?

Accepted Answer

try: read_file() except UnicodeDecodeError: log.warning('Skipping file'). It catches only UnicodeDecodeError, which is the specific exception raised when a file contains invalid UTF-8 or other encoding issues. It logs a warning and then continues execution (the 'pass' is implied by the log statement, but the key is that the exception is handled without re-raising). This matches the requirement to skip the file without stopping the entire process.

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try: read_file() except (UnicodeDecodeError, OSError): pass

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try: read_file() except Exception: log.warning('Skipping file')

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try: read_file() except UnicodeEncodeError: log.warning('Skipping file')

Question 4

A developer needs to write binary data to a file. Which file mode should be used to open the file for writing in binary mode without truncating it if it already exists?

Accepted Answer

'ab'. ('ab') is correct because the 'a' mode opens the file for appending, which writes data at the end without truncating the existing content, and adding 'b' specifies binary mode. This allows binary data to be written to a file that already exists without losing its current contents.

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'wb'

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'rb'

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'wb+'

Question 5

A developer has a function that performs several operations and may raise different exceptions. The developer wants to catch a specific exception and then re-raise it after logging. Which code snippet correctly re-raises the same exception without losing its traceback?

Accepted Answer

except ValueError as e: log.error(e); raise. Using a bare `raise` statement inside an `except` block re-raises the original exception instance, preserving its full traceback. This is the standard Python idiom for logging an exception and then propagating it unchanged, ensuring that the original call stack and error context are not lost.

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except ValueError as e: log.error(e); return None

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except ValueError as e: log.error(e); raise ValueError('New')

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except ValueError as e: log.error(e); pass

Question 6

A developer is working on a data pipeline that processes files from untrusted sources. The pipeline should catch and log any exception, but also ensure that sensitive information from the exception (e.g., file paths) is not exposed to end users. Which approach balances security and debugging?

Accepted Answer

Catch the exception, log the full traceback, then raise a custom generic exception.. It balances security and debugging: the full traceback is logged for developers (preserving debugging details like file paths), while a custom generic exception is raised to end users, preventing sensitive information from being exposed. This approach follows the principle of least privilege for error handling, ensuring that internal details are not leaked to untrusted sources.

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Catch the exception and re-raise the same exception.

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Catch the exception, log it, and suppress it silently.

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Catch the exception and print it to the console.

Question 7

A developer is building a logging system that writes logs to a file. The system should handle disk-full situations gracefully without crashing the main application. Which approach is appropriate?

Accepted Answer

Wrap the log write in a try/except that catches OSError and writes to stderr as fallback.. It uses a targeted try/except block around only the log write operation, catching OSError (which includes disk-full conditions) and falling back to stderr. This prevents the main application from crashing while still reporting the error, adhering to the principle of handling exceptions at the point where they occur and only when you can meaningfully recover.

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Check disk space before each write; if low, skip logging.

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Wrap the entire application in a try/except that catches all exceptions.

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Let the OSError propagate to the main program's exception handler.

Question 8

A developer is creating a custom exception hierarchy for a library. The base exception is `LibraryError`. Which definition ensures that subclasses can be caught using the parent exception, but also allows distinguishing between different error types?

Accepted Answer

class LibraryError(Exception): pass
class FileError(LibraryError): pass
class ParseError(LibraryError): pass. It defines `LibraryError` as a subclass of `Exception`, which is the proper base class for all user-defined exceptions in Python. Subclasses `FileError` and `ParseError` inherit from `LibraryError`, so they can be caught with `except LibraryError` while still being distinguishable by their own type. This follows the standard Python exception hierarchy, where custom exceptions should derive from `Exception`, not `BaseException` or no base class.

Answer

class LibraryError: pass
class FileError(LibraryError): pass
class ParseError(LibraryError): pass

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class LibraryError(BaseException): pass
class FileError(LibraryError): pass
class ParseError(LibraryError): pass

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class LibraryError(Exception): pass
class FileError(Exception): pass
class ParseError(Exception): pass

Question 9

Which TWO statements about exception handling in Python are correct? (Select exactly 2.)

Accepted Answer

A single except clause can catch multiple exception types by passing a tuple of exceptions.. Python's except clause accepts a tuple of exception types, allowing a single handler to catch multiple exception types. For example, `except (ValueError, TypeError):` will catch either exception, which is a concise way to handle related errors without duplicating code.

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The order of except clauses does not matter because only one will match.

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An else block can be used without any except blocks in a try statement.

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The else block in a try statement executes only if an exception was raised.

Question 10

Which TWO of the following are built-in exceptions in Python? (Select exactly 2.)

Accepted Answer

ValueError. ValueError is a built-in exception in Python, raised when a built-in operation or function receives an argument with the correct type but an inappropriate value, such as int('abc'). It is part of Python's standard exception hierarchy and does not require any import.

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InputError

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DataError

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CustomError

Question 11

Refer to the exhibit. A developer ran the script and saw the above traceback. The intended behavior was to load a JSON configuration file, and if the file is missing, create a default config. What is the most likely root cause of the second exception (NameError)?

Accepted Answer

The script did not import the json module.. The traceback shows a NameError for 'json.loads', which indicates that the name 'json' is not defined in the current namespace. This occurs when the script attempts to call json.loads() without first importing the json module. The intended behavior of loading a JSON configuration file requires the json module to parse the file content, and its absence causes the NameError exception.

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The variable 'f' was not defined due to the FileNotFoundError.

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The config.json file exists but is empty.

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The file was opened in binary mode instead of text mode.

Question 12

Refer to the exhibit. A developer is writing a script to read this JSON configuration file. The script should write the logging configuration to a separate file called 'logging.conf'. Which file mode should be used to create the file if it doesn't exist, and overwrite it if it does?

Accepted Answer

'w'. ('w') is correct because the 'w' mode opens a file for writing, truncating it first if it exists, and creating it if it does not. This matches the requirement to overwrite an existing 'logging.conf' file or create a new one if absent.

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'x'

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'r+'

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'a'

Question 13

Refer to the exhibit. The above log shows an unhandled exception that caused the program to crash. The developer wants to handle this exception and log the error without crashing. Which exception type should be caught in the main code to capture this specific error?

Accepted Answer

ValueError. The traceback shows that a ValueError was raised. To handle this specific exception, the code should catch ValueError. Catching Exception would also work but is less specific. Catching BaseException catches system-exit exceptions. OSError is unrelated.

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BaseException

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OSError

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Exception

Question 14

A developer writes a script that reads a configuration file. If the file does not exist, the program should print an error and continue. Which code snippet correctly implements this behavior?

Accepted Answer

try: open('config.txt') except FileNotFoundError: print('File not found'). It uses a `try` block to attempt opening the file and catches only `FileNotFoundError`, which is the specific exception raised when the file does not exist. This allows the program to print an error and continue execution without crashing, precisely matching the requirement.

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f = open('config.txt', 'r') if not f: print('File not found')

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try: f = open('config.txt') except: print('File not found')

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try: with open('config.txt') as f: pass except Exception: print('File not found')

Question 15

Which of the following is the correct way to open a file for writing in binary mode?

Accepted Answer

open('data.dat', 'wb'). The mode string 'wb' specifies both write ('w') and binary ('b') mode, which is the proper way to open a file for writing binary data in Python. The order of characters in the mode string is fixed: the file mode character ('r', 'w', 'a', etc.) must come first, followed by the optional 'b' for binary mode.

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open('data.dat', 'bw')

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open('data.dat', 'br')

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open('data.dat', 'w')