PCAP Exceptions and File I/O Practice Test 5 — 15 Questions

Question 1

Refer to the exhibit. If 'data.txt' contains '123', what is the output?

Accepted Answer

No output. The code attempts to open 'data.txt' in write mode ('w'), which creates a new empty file or truncates an existing one. Since the file is opened for writing, no data is read from it, and the print() call is outside the with block, so it executes after the file is closed. The output is 'No output' because the code does not print anything from the file.

Answer

123

Answer

Error: invalid literal for int()

Answer

Error: [Errno 2] No such file or directory

Question 2

Refer to the exhibit. If /var/data/in.csv does not exist, what exception is raised?

Accepted Answer

FileNotFoundError. When a file does not exist and you attempt to open it for reading using the built-in `open()` function, Python raises a `FileNotFoundError`. This is a subclass of `OSError` and is the standard exception for missing files in Python 3. The question explicitly states that `/var/data/in.csv` does not exist, so the correct exception is `FileNotFoundError`.

Answer

configparser.NoSectionError

Answer

PermissionError

Answer

IndexError

Question 3

Refer to the exhibit. What is the output of this code?

Accepted Answer

OS error. The question asks for the output of code shown in an exhibit, but the exhibit is missing. Without the actual try/except structure and the print statements in each except block, it is not possible to determine whether the output is 'OS error' or something else. The explanation only states that FileNotFoundError is caught by the first except block, but it does not state what that block outputs.

Answer

No output

Answer

Traceback with FileNotFoundError

Answer

File not found

Question 4

Refer to the exhibit. What is the output?

Accepted Answer

A D. The code defines a custom exception class `MyError` that inherits from `Exception`, and the `try` block raises `MyError` with the message 'A'. The first `except` clause catches `MyError` and prints 'A', then the `else` clause is skipped because an exception was raised, and the `finally` clause always executes, printing 'D'. Thus the output is 'A D'.

Answer

A C D

Answer

A

Answer

B D

Question 5

A developer implements a custom exception class `DataError` that inherits from `Exception`. Which method override is essential to ensure the exception message is properly displayed when caught?

Accepted Answer

Override __init__ to accept a message and call super().__init__(message).. The `Exception` class's `__init__` method stores the message argument in the `args` attribute, which is used by the default `__str__` method to display the message. By overriding `__init__` to accept a message and call `super().__init__(message)`, the custom exception properly passes the message to the base class, ensuring it is displayed when caught and printed.

Answer

Set the __cause__ attribute in __init__.

Answer

Override __str__ to return a formatted string.

Answer

Override __repr__ to return a detailed representation.

Question 6

Which of the following statements about the `finally` block is true?

Accepted Answer

It always executes, regardless of exceptions.. The `finally` block in Python is designed to always execute after the `try` and `except` blocks, regardless of whether an exception was raised or not. This includes cases where a `return`, `break`, or `continue` statement is executed in the `try` block, or even if an unhandled exception occurs. The `finally` block is guaranteed to run before the function returns or the exception propagates, ensuring cleanup actions like closing files or releasing resources.

Answer

It executes only if no exception is raised.

Answer

It does not execute if a return statement is in try block.

Answer

It executes only if an exception is raised.

Question 7

What is the output of the Python code after reading the config.txt file?

Accepted Answer

8080. The code reads the config.txt file and splits its content by newlines. The first line contains 'port=8080', and after splitting by '=', the second element is '8080'. The int() function converts this string to the integer 8080, which is then printed. Option C is correct because the output is the integer 8080, not a string or quoted form.

Answer

8080 (as string)

Answer

An exception is raised.

Answer

'8080'

Question 8

Drag and drop the steps to serialize a Python object to JSON using the json module into the correct order.

Accepted Answer

Step 1: Import the json module. Step 2: Create a Python dictionary. Step 3: Open a file in write mode. Step 4: Use json.dump() to write the dictionary to the file.. Serialization to JSON involves importing json, preparing data, using dumps for string or dump for file output.

Answer

Step 1: Create a Python dictionary. Step 2: Import the json module. Step 3: Open a file in write mode. Step 4: Use json.dump() to write the dictionary to the file.

Answer

Step 1: Import the json module. Step 2: Open a file in write mode. Step 3: Create a Python dictionary. Step 4: Use json.dump() to write the dictionary to the file.

Answer

Step 1: Import the json module. Step 2: Create a Python dictionary. Step 3: Use json.dump() to write the dictionary to the file. Step 4: Open a file in write mode.

Question 9

Match each Python data structure to its mutability.

Accepted Answer

list: Mutable. In Python, list, dict, and set are mutable data structures, meaning their contents can be modified. Tuple, string, and frozenset are immutable; their contents cannot be changed after creation. Common confusions include thinking tuples are mutable (they are not) or that frozensets are mutable (they are not).

Answer

tuple: Mutable

Answer

set: Immutable

Answer

frozenset: Mutable

Question 10

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.

Answer

PermissionError

Answer

IOError

Answer

OSError

Question 11

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.

Answer

Catch the exception and re-raise the same exception.

Answer

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

Answer

Catch the exception and print it to the console.

Question 12

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.

Answer

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

Answer

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

Answer

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

Question 13

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

Answer

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

Answer

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

Question 14

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.

Answer

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

Answer

The config.json file exists but is empty.

Answer

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

Question 15

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.

Answer

'x'

Answer

'r+'

Answer

'a'