PCAP Practice Test 5 — 10 Questions

Question 1

A programmer writes a class with a method that should be called on the class itself, not on instances. Which decorator is appropriate?

Accepted Answer

@classmethod. The @classmethod decorator transforms a method so that it receives the class itself as the first implicit argument (cls), rather than an instance (self). This allows the method to be called on the class directly, e.g., MyClass.my_method(), and is the correct choice when a method should operate on the class level, not on instances.

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@property

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@abstractmethod

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@staticmethod

Question 2

A developer needs to count the number of occurrences of the substring 'is' in the string 'This is a test. Is this a test?'. Which code correctly performs the count?

Accepted Answer

'This is a test. Is this a test?'.count('is'). Python's string method `count(substring)` returns the number of non-overlapping occurrences of the substring in the string. In 'This is a test. Is this a test?', 'is' appears twice (in 'This' and 'is'), and the method counts them correctly, ignoring case sensitivity (the capitalized 'Is' is not counted).

Answer

'This is a test. Is this a test?'.split().count('is')

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'This is a test. Is this a test?'.index('is')

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'This is a test. Is this a test?'.find('is')

Question 3

A class has a class attribute that is a list. A developer modifies this list via one instance, and the change is reflected in all other instances. What is the best practice to avoid this unintended sharing?

Accepted Answer

Initialize the list in `__init__` rather than as a class attribute.. Class attributes are shared across all instances. By initializing the list inside `__init__`, each instance gets its own independent list object, preventing unintended mutation from affecting other instances. This is the standard Python pattern for instance-specific mutable data.

Answer

Use a tuple instead of a list.

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Use a class method to modify the list.

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Use `deepcopy` when accessing the list.

Question 4

A senior developer in a team argues that using try-except blocks is slower than checking conditions with if statements. They propose replacing all try blocks that handle file I/O errors with existence checks using os.path.exists before opening files. During a code review, you recall that Python's official documentation and best practices prefer EAFP (Easier to Ask for Forgiveness than Permission) over LBYL (Look Before You Leap) in many cases, especially in concurrent environments. The team's application is a multi-threaded web server that serves static files from a shared directory. Which is the strongest counterargument against the senior developer's proposal?

Accepted Answer

LBYL leads to race conditions in concurrent code because the file's state can change between the check and the use.. In a multi-threaded web server, the LBYL approach (checking with os.path.exists) introduces a classic TOCTOU (Time of Check, Time of Use) race condition: between the existence check and the actual file open, another thread could delete or rename the file, causing the open to fail despite the check passing. Python's EAFP idiom (try-except) avoids this window by attempting the operation directly and handling the exception if it fails, which is inherently atomic with respect to the file system state. This is why official Python documentation recommends EAFP over LBYL in concurrent environments.

Answer

if statements are harder to read and maintain.

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try-except can catch multiple exception types more cleanly.

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try-except blocks have no performance cost at all.

Question 5

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.

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

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The else clause is used to specify additional exception handlers.

Question 6

Which of the following demonstrates that strings are immutable?

Accepted Answer

s[0] = 'J' results in a TypeError. Attempting to assign a new character to an index of a string (e.g., s[0] = 'J') raises a TypeError, which directly demonstrates that strings are immutable in Python. Immutability means the object's value cannot be changed after creation; any operation that appears to modify a string actually creates a new string object.

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s.upper() changes s in place

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s += '!' modifies s

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s.replace('a','b') modifies s

Question 7

A developer needs to parse a log file where each line contains a timestamp followed by a message. The timestamp format is 'YYYY-MM-DD HH:MM:SS'. Which string method is most appropriate to split the timestamp from the message?

Accepted Answer

str.split(). Str.split(), is the most appropriate because it splits a string on whitespace by default. Although the timestamp 'YYYY-MM-DD HH:MM:SS' contains a space, using split() without arguments returns a list of all space-separated elements. Since the timestamp is always the first two elements (date and time), the developer can join them with a space to get the full timestamp. Alternatively, split() can be used with a specified separator and maxsplit to achieve the desired split. This flexibility makes str.split() the best choice among the given options.

Answer

str.rsplit()

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str.splitlines()

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str.partition()

Question 8

A developer wants a class 'LoggedDict' that behaves like a dict but logs all attribute access in the console. Which method override correctly implements this for getting an attribute?

Accepted Answer

def __getattribute__(self, name): print(f'Access {name}'); return super().__getattribute__(name). `__getattribute__` is the universal method called for every attribute access on an object. By overriding it, the developer can log the attribute name before delegating to the superclass implementation via `super().__getattribute__(name)`, which preserves the normal attribute lookup chain. This ensures that all attribute accesses (including those that exist and those that don't) are logged, which is the requirement for 'LoggedDict'.

Answer

def __get__(self, instance, owner): print(f'Access'); return self

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def __getattr__(self, name): print(f'Access {name}'); return self.__dict__[name]

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def __getitem__(self, key): print(f'Access {key}'); return dict.__getitem__(self, key)

Question 9

A function receives a file path like '/home/user/docs/file.txt' and needs to return the path without the file extension, e.g., '/home/user/docs/file'. Which code reliably removes only the last dot extension, even if the directory names contain dots?

Accepted Answer

path.rsplit('.', 1)[0]. `rsplit('.', 1)` splits the string from the right, limiting the split to exactly one occurrence, which isolates the file extension (the part after the last dot) and returns everything before it. This reliably removes only the last dot extension, even if directory names contain dots, because it targets the final dot in the path.

Answer

path.split('.')[0]

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path.replace('.', '', 1)

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path[:path.find('.')]

Question 10

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'

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'r+'

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'a'