PCAP Exceptions and File I/O Practice Test 2 — 15 Questions

Question 1

Refer to the exhibit. If 'data.txt' does not exist, what happens?

Accepted Answer

A NameError is raised because f is not defined in the finally block.. In Python, the variable `f` is assigned inside the `try` block (via `open('data.txt', 'r')`). If the file does not exist, a `FileNotFoundError` is raised before the assignment completes, so `f` is never defined. The `finally` block then attempts to call `f.close()`, which references an undefined name, raising a `NameError`. This occurs because the `finally` block executes regardless of exceptions, but the variable `f` was never bound in the local scope.

Answer

The function returns None.

Answer

A FileNotFoundError is raised and not caught.

Answer

The file is created and then closed.

Question 2

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 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 writes a function that reads a configuration file and returns its contents as a string. The file might not exist. Which exception should be caught to handle a missing file?

Accepted Answer

FileNotFoundError. `FileNotFoundError` is a built-in exception in Python that is raised when a file or directory is requested but does not exist. In Python 3, file-related I/O errors are organized under `OSError` with specific subclasses, and `FileNotFoundError` is the precise exception for a missing file, making it the most appropriate catch for this scenario.

Answer

PermissionError

Answer

IOError

Answer

OSError

Question 6

Which of the following is the correct way to open a file for writing in text mode, ensuring that if the file already exists it will be overwritten?

Accepted Answer

open('file.txt', 'w'). The 'w' mode opens the file for writing in text mode and truncates the file to zero length if it exists, or creates a new file if it does not. This ensures any existing content is overwritten, which matches the requirement.

Answer

open('file.txt', 'x')

Answer

open('file.txt', 'r+')

Answer

open('file.txt', 'a')

Question 7

A script uses `with open('data.bin', 'rb') as f:` to read binary data. Within the block, which method should be used to read exactly 4 bytes?

Accepted Answer

f.read(4). The `read(n)` method reads exactly `n` bytes from the file object when the file is opened in binary mode (`'rb'`). Since the question specifies reading exactly 4 bytes, `f.read(4)` is the correct and direct approach. This method returns a bytes object of up to `n` bytes, but if the file has at least 4 bytes remaining, it will return exactly 4.

Answer

f.seek(4)

Answer

f.readline()

Answer

f.read()

Question 8

Consider the following code snippet:

try:
    x = int(input())
    y = 10 / x
    print(y)
except ZeroDivisionError:
    print('Division by zero')
except ValueError:
    print('Invalid integer')

If the user enters '0', what is the output?

Accepted Answer

Division by zero. When the user enters '0', the input is successfully converted to the integer 0 by int(), so no ValueError occurs. Then 10 / 0 raises a ZeroDivisionError, which is caught by the except ZeroDivisionError block, printing 'Division by zero'. Option C is correct because the code never reaches the ValueError handler.

Answer

No output

Answer

Both 'Invalid integer' and 'Division by zero'

Answer

Invalid integer

Question 9

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 10

A programmer wants to catch both `FileNotFoundError` and `PermissionError` with a single except clause. Which tuple is correct?

Accepted Answer

except (FileNotFoundError, PermissionError):. Python's exception handling syntax allows a tuple of exception types in a single `except` clause, enabling the programmer to catch multiple exception types with the same handler. Both `FileNotFoundError` and `PermissionError` are subclasses of `OSError`, but using the tuple explicitly catches only those two specific exceptions, not all `OSError` subtypes.

Answer

except FileNotFoundError, PermissionError:

Answer

except OSError:

Answer

except [FileNotFoundError, PermissionError]:

Question 11

Which THREE of the following are true about the `with` statement for file handling?

Accepted Answer

It uses the __enter__ and __exit__ methods of the file object.. The `with` statement relies on the context management protocol, which requires the object to implement the `__enter__` and `__exit__` methods. When a file object is used with `with`, its `__enter__` method returns the file object itself, and its `__exit__` method is called upon block exit to handle cleanup, such as closing the file.

Answer

It can only be used with files.

Answer

It can only handle one file at a time.

Question 12

Which TWO of the following are built-in Python exceptions?

Accepted Answer

ValueError. ValueError (C) is a built-in Python exception that is raised when a built-in operation or function receives an argument with the correct type but an inappropriate value, such as int('abc'). FileNotFoundError (D) is a built-in exception in Python 3, raised when a file or directory is requested but does not exist, commonly encountered during file I/O operations like open().

Answer

CustomException

Answer

InputError

Answer

FileReadError

Question 13

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 14

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 15

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