PCAP Exceptions and File I/O Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✓

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

  Why this is correct

  This snippet is correct because it confines the error handling to exactly the condition the developer cares about: the file's absence. When the interpreter evaluates open('config.txt'), a missing config file raises a FileNotFoundError (a subclass of OSError), and that exception is caught and handled specifically. Other I/O problems, such as a permission denial or a path that is actually a directory, raise different OSError subclasses and are allowed to propagate, which preserves diagnostic accuracy.

• ✗

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

  Why it's wrong here

  The flaw in this option is its false premise about open()'s failure behavior. In Python, open() never returns None or False when it cannot find a file; it always raises an exception, specifically FileNotFoundError. If the file does not exist, the exception occurs on the first line and the script aborts before the if not f condition can ever be evaluated. Conversely, after a successful open(), the returned file object is always truthy, so the condition would never trigger even if the file existed.

• ✗

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

  Why it's wrong here

  Using a bare except: clause is an anti-pattern because it intercepts every exception type, including KeyboardInterrupt and SystemExit, which are BaseException subclasses rather than regular Exception subclasses. Although this code will successfully suppress FileNotFoundError, it will also silently hide memory errors and other critical conditions that a developer almost certainly wants to see. In addition, if the try block ever grows to contain more than just open(), the bare handler masks unrelated bugs, making the message 'File not found' misleading.

• ✗

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

  Why it's wrong here

  This variant wraps the file access in a context manager, which is good for resource cleanup, but pairs it with an overly broad except Exception handler. Because FileNotFoundError is a subclass of Exception, the handler does catch the intended case, but it also catches any other Exception raised inside the with body or while exiting the manager. For example, if config-file parsing code in the with block later raises a ValueError or KeyError, the script will incorrectly print 'File not found', turning a genuine logic bug into a misleading diagnostic.

Go deeper

Related to this question