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

Question 1

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.

Answer

'wb'

Answer

'rb'

Answer

'wb+'

Question 2

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.

Answer

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

Answer

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

Answer

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

Question 3

A developer writes a script that opens a file for reading. The script must ensure that the file is closed even if an exception occurs during reading. Which pattern guarantees proper resource cleanup?

Accepted Answer

file = open('data.txt'); try: # read; finally: file.close(). Both option A and option C guarantee that the file is closed if an exception occurs during reading. Option A uses try/finally, which executes finally even on exceptions, and since the open() succeeds before the try block, there is no NameError. Option C uses the with statement, which is the recommended Pythonic approach and also guarantees cleanup via the context manager protocol.

Answer

file = open('data.txt'); # read; file.close()

Answer

file = open('data.txt'); if not file.closed: file.close()

Question 4

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.

Answer

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

Answer

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

Answer

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

Question 5

Consider the following code snippet:

x = [1, 2, 3]
try:
    print(x[5])
except IndexError:
    print('Index')
except LookupError:
    print('Lookup')

Which THREE statements about this code are correct? (Select exactly 3.)

Accepted Answer

If the line with IndexError is removed, then LookupError will catch the exception.. Options B, C, and E are correct. Option B is true because removing IndexError leaves LookupError to catch the exception. Option C is a fact about Python's exception hierarchy. Option E matches the actual output. Option D is not about the given code; it discusses a hypothetical scenario that is not part of the code snippet.

Answer

The code will print 'Lookup' because LookupError is more general.

Answer

If the code were accessing a dictionary key, LookupError would catch KeyError.

Question 6

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.

Answer

InputError

Answer

DataError

Answer

CustomError

Question 7

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.

Answer

BaseException

Answer

OSError

Answer

Exception

Question 8

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.

Answer

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

Answer

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

Answer

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

Question 9

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.

Answer

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

Answer

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

Answer

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

Question 10

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 11

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 12

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 13

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 14

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 15

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