PCAP Exceptions and File I/O Practice Test 4 — 15 Questions

Question 1

Which method of a file object reads the entire content of a text file as a single string?

Accepted Answer

read(). The `read()` method, when called without arguments or with a negative size, reads the entire contents of a file as a single string. This is the standard Python file object method for reading all text at once, returning a str object. It is the correct choice because the question explicitly asks for a method that returns the entire content as a single string.

Answer

readall()

Answer

readline()

Answer

readlines()

Question 2

What is the output of the following code?

try:
    print(1/0)
except:
    print('err')
finally:
    print('fin')

Accepted Answer

err fin. When a division by zero occurs, Python raises a ZeroDivisionError, which is caught by the bare except clause, printing 'err'. The finally clause always executes after the except block, printing 'fin'. Thus the output is 'err' followed by 'fin'.

Answer

fin err

Answer

fin

Answer

err

Question 3

A developer wants to ensure that a file is always closed after writing, even if an exception occurs. Which approach is considered best practice in Python?

Accepted Answer

Use the with statement: with open('file.txt', 'w') as f: .... The `with` statement in Python implements a context manager that automatically calls the file's `__exit__` method, which closes the file even if an exception occurs inside the block. This is the idiomatic and recommended approach for resource management, as it guarantees cleanup without requiring explicit `close()` calls.

Answer

Use try/finally with explicit f.close()

Answer

Rely on the garbage collector to close the file

Answer

Use try/except/finally with f.close() in both except and finally

Question 4

A file is opened with open('test.txt', 'r'). The file object's tell() method returns 0. After reading 10 characters, what does tell() return?

Accepted Answer

10. The `tell()` method returns the current position of the file pointer in bytes from the beginning of the file. After reading 10 characters (each being 1 byte in a typical text file), the pointer advances by 10 bytes, so `tell()` returns 10.

Answer

File size

Answer

0

Answer

-1

Question 5

What is the output of the following code?

try:
    raise ValueError('a')
except ValueError as e:
    print(e.args[0])
finally:
    print('b')

Accepted Answer

a
b. The `finally` block always executes after the `try` block, even when an exception is raised. The `except` block catches the `ValueError` and prints the first argument of the exception (`'a'`), then the `finally` block prints `'b'`. The output is `a` on one line and `b` on the next, matching `a
b`.

Answer

a b

Answer

b a

Answer

b

Question 6

Which of the following correctly raises a new exception while preserving the original traceback?

Accepted Answer

raise ValueError('new') from original_exception. The `raise ... from original_exception` syntax in Python allows you to raise a new exception while chaining it to the original exception, preserving the original traceback. This is essential for debugging, as it shows both the new error and the root cause.

Answer

raise original_exception

Answer

raise ValueError('new')

Answer

raise

Question 7

What is the output of the following code?

try:
    exec('1/0')
except:
    print('error')
else:
    print('no error')
finally:
    print('done')

Accepted Answer

error done. The `exec('1/0')` raises a `ZeroDivisionError`, which is caught by the bare `except:` clause, printing 'error'. The `else` clause is skipped because an exception occurred, but the `finally` clause always executes, printing 'done'. Thus the output is 'error' followed by 'done'.

Answer

done error

Answer

error

Answer

done

Question 8

Which TWO of the following are appropriate techniques for logging exception details in Python? (Select exactly 2)

Accepted Answer

Using traceback.format_exc(). `traceback.format_exc()` returns the full traceback as a string, which can be logged or printed to capture detailed exception context. Option E is correct because `logging.exception()` automatically includes the traceback of the current exception when called inside an `except` block, making it the idiomatic way to log exceptions in Python.

Answer

Using print(e.args)

Answer

Using sys.exc_info()

Answer

Using raise without argument

Question 9

Which THREE of the following statements about Python's 'with' statement are true? (Select exactly 3)

Accepted Answer

It can be used with any object that implements __enter__ and __exit__ methods.. Option A is correct because the context manager protocol is defined precisely by the presence of __enter__ and __exit__ methods, so any object implementing both can be used with 'with'. Option B is correct because the 'with' statement's semantics ensure __exit__ is invoked when the block exits, whether normally or via an exception, which is the core guarantee of the protocol. Option C is correct because Python supports 'with A() as a, B() as b:' syntax, allowing multiple context managers separated by commas (equivalent to nested with statements). Option D is not marked correct because while 'with' often replaces try/finally for resource cleanup, it does not eliminate the need for try/finally in all cases, such as when no context manager exists or when cleanup logic must run without one. Option E is not marked correct because 'with' works with any context manager, not only file objects; files are just a common example.

Answer

It eliminates the need for try/finally blocks for resource management.

Answer

It can only be used with file objects.

Question 10

Refer to the exhibit. If the file config.cfg exists but the user does not have read permission, what will be printed?

Accepted Answer

'Permission denied'. When `open()` is called on a file that exists but the user lacks read permission, Python raises a `PermissionError`. Since no exception handling is present, the exception is unhandled and Python prints a traceback to stderr which includes the error message `'Permission denied'` (among other details). Option B correctly identifies the permission-denied message that appears in the output.

Answer

An unhandled exception is raised

Answer

Nothing; the program continues silently

Answer

'File not found'

Question 11

Refer to the exhibit. Which of the following Python code snippets would generate this error?

Accepted Answer

int('abc'). `int('abc')` attempts to convert the string `'abc'` to an integer, which is not a valid numeric literal. Python raises a `ValueError` with the message 'invalid literal for int() with base 10: 'abc''. This error occurs because the `int()` function expects a string that represents a valid integer in the specified base (default base 10), and 'abc' does not meet that criterion.

Answer

str(123)

Answer

print('abc')

Answer

float('abc')

Question 12

Refer to the exhibit. If both data.txt and backup.txt do not exist, what is the output?

Accepted Answer

'No file found'. The code uses a try-except block to catch FileNotFoundError when attempting to open 'data.txt'. In the except block, it prints 'No file found' and then attempts to open 'backup.txt'. Since both files do not exist, the except block executes and prints 'No file found' before the second open attempt raises another FileNotFoundError, which is unhandled and terminates the program. However, the question asks for the output, which is the print statement executed before the error.

Answer

Prints contents of backup.txt

Answer

Nothing

Answer

FileNotFoundError

Question 13

In Python, if you have a try block followed by an except clause that catches all exceptions, which of the following is true about the else clause?

Accepted Answer

The else clause runs only if no exception is raised in the try block.. In Python, the `else` clause in a `try` statement executes only if no exception was raised in the `try` block. This is true regardless of whether the `except` clause catches all exceptions (e.g., bare `except:` or `except Exception:`). The `else` block is specifically designed for code that should run only when the `try` block completes successfully without any exception.

Answer

The else clause runs only if an exception occurs.

Answer

The else clause runs before the finally block regardless of exceptions.

Answer

The else clause is used to specify additional exception handlers.

Question 14

A developer needs to write a function that safely divides two numbers and returns None if division by zero occurs. Which implementation is most Pythonic?

Accepted Answer

def safe_divide(a, b):
    try:
        return a/b
    except ZeroDivisionError:
        return None. It uses a try-except block to catch the specific ZeroDivisionError that Python raises when dividing by zero. This is the most Pythonic approach, following the EAFP (Easier to Ask for Forgiveness than Permission) principle, which is preferred over LBYL (Look Before You Leap) in Python. The function returns None only when the exception occurs, preserving the natural behavior of division for all other cases.

Answer

def safe_divide(a, b):
    return a/b if b else None

Answer

def safe_divide(a, b):
    if b != 0:
        return a/b
    else:
        return None

Answer

def safe_divide(a, b):
    try:
        return a/b
    except ValueError:
        return None

Question 15

Consider the code fragment: 
    f = open('data.txt', 'r')
    data = f.read()
    process_data(data)
    f.close()
What is the primary risk if an exception occurs during process_data(data)?

Accepted Answer

The file descriptor may be leaked because the close() call is skipped.. If `process_data(data)` raises an exception, the `f.close()` statement is never executed, leaving the file descriptor open. This is a resource leak that can exhaust system file handles, especially in long-running applications. Python's `with` statement is the recommended approach to guarantee automatic cleanup even when exceptions occur.

Answer

The exception will be silently suppressed.

Answer

The file will be automatically closed by Python's garbage collector immediately.

Answer

The file contents will be corrupted.