PCAP Practice Test 5 — 25 Questions

Question 1

A class inherits from two parent classes that both have a method with the same name. When calling the method on the child, only one parent's version is executed. What Python mechanism determines which one?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

Method Resolution Order (MRO).. Python uses the C3 linearization algorithm to compute the Method Resolution Order (MRO) for a class. When a method is called on an instance, Python searches the MRO from left to right and executes the first implementation it finds. This ensures a consistent and predictable order of inheritance, even in diamond or multiple-inheritance scenarios.

Answer

Method overloading by signature.

Answer

Explicit super() call in the child class.

Answer

Inheritance depth (closest parent wins).

Question 2

A Python script imports the module 'my_module'. The developer wants to ensure that when the script is run directly, it executes a specific function, but when imported as a module, that function is not executed. Which code snippet achieves this?

Accepted Answer

if __name__ == '__main__': run(). Both options A and B are correct because they are identical and represent the standard Python idiom `if __name__ == '__main__': run()`. When the script is run directly, Python sets `__name__` to `'__main__'`, triggering the function. When imported, `__name__` is the module name, so the function is not executed. Options C and D are incorrect: C relies on an environment variable that is not standard, and D checks `sys.argv[0]` which is the script path, not the module name.

Answer

if os.environ.get('RUN_MAIN'): run()

Answer

if sys.argv[0] == 'my_module': run()

Question 3

Drag and drop the steps to handle an exception in Python using try-except-finally into the correct order.

Accepted Answer

try block, then except block(s), then else block, then finally block. Exception handling follows the order: try block, except blocks, else block, finally block. The raise statement can be used anywhere to trigger an exception.

Answer

try block, then except block(s), then finally block, then else block

Answer

try block, then else block, then except block(s), then finally block

Answer

else block, then try block, then except block(s), then finally block

Question 4

Which THREE of the following escape sequences are valid in a Python string and represent a single character? (Select exactly three.)

Accepted Answer

\'. The backslash followed by a single quote (\') is a valid escape sequence in Python that represents a literal single quote character, allowing it to appear inside a single-quoted string without terminating the string. This sequence is interpreted as a single character by the Python parser.

Answer

\x

Answer

\q

Question 5

A development team is building a real-time chat application using Python. The application uses a class 'ChatRoom' that maintains a list of 'User' objects as active participants. Each User object holds a reference back to its ChatRoom to send messages. Over time, the application runs out of memory. Profiling reveals that User objects are not being garbage collected even after users disconnect. The team suspects circular references. Which solution would effectively resolve the memory leak without breaking the functionality?

Accepted Answer

Use weakref.WeakSet for the participants list in ChatRoom, so that when a User is no longer referenced elsewhere, it is automatically removed. Using a `weakref.WeakSet` for the participants list in `ChatRoom` means the `ChatRoom` holds only weak references to `User` objects. When a user disconnects and all external references to that `User` are removed, the `User` object becomes unreachable and can be garbage collected, even though the `User` still holds a strong reference back to the `ChatRoom`. This breaks the circular reference without requiring manual intervention or altering the `User`-to-`ChatRoom` relationship.

Answer

Increase the Python heap size using PYTHON_MALLOC_DEBUG to avoid memory issues

Answer

Store the ChatRoom reference in User using a weakref.ref, so that the cycle is broken

Answer

Manually call gc.collect() every time a user disconnects

Question 6

A developer is tasked with validating user input that must be a 10-digit phone number. The input may contain spaces, dashes, and parentheses. Which approach best ensures the input contains exactly 10 digits?

Accepted Answer

if len([c for c in s if c.isdigit()]) == 10:. Uses a list comprehension to filter only digit characters from the input string `s` and then checks if the count of those digits is exactly 10. This correctly handles any non-digit characters (spaces, dashes, parentheses) by ignoring them, ensuring the validation focuses solely on the presence of exactly ten digits.

Answer

if len(s) >= 10 and s.isdigit():

Answer

if s[:10].isdigit():

Answer

if s.isdigit() and len(s) == 10:

Question 7

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 8

A Python script is written to be used both as a standalone program and as an imported module. Which condition should the script use to execute code only when run directly?

Accepted Answer

if __name__ == '__main__':. Python sets the global variable `__name__` to `'__main__'` when the script is executed directly (e.g., `python script.py`). When the script is imported as a module, `__name__` is set to the module's name. The condition `if __name__ == '__main__':` is the standard Python idiom to guard code that should only run in the direct execution context.

Answer

if __import__ == '__main__':

Answer

if __name__ == '__module__':

Answer

if __file__ == 'main':

Question 9

A company has a large Python application that uses multiple packages from different directories. The application's main entry point is at /opt/app/main.py. There is a package 'common' located at /opt/app/common/ and another package 'services' at /opt/app/services/. Both packages have __init__.py files. Additionally, there is a third-party package 'utils' installed in the system site-packages. Recently, a developer added a new module 'helpers.py' to the 'common' package. When trying to import 'common.helpers' from a script inside 'services', an ImportError is raised: 'No module named common.helpers'. However, importing 'common' itself works. The sys.path includes /opt/app/ and the site-packages. What is the most likely cause of the import failure?

Accepted Answer

There is another 'common' package elsewhere in sys.path that shadows the intended one, and the shadowed package does not have a 'helpers' submodule.. The most likely cause is that a different 'common' package (without a 'helpers' submodule) appears earlier in sys.path and shadows the intended /opt/app/common/ package. Since sys.path includes /opt/app/ and site-packages, if a 'common' package exists in site-packages or another directory listed before /opt/app/, Python will import that shadowed package instead, and it lacks the newly added 'helpers' module. This explains why importing 'common' succeeds (the shadowed package exists) but 'common.helpers' fails.

Answer

The 'helpers.py' file was added after the Python interpreter started, and sys.modules caching prevents new imports.

Answer

The PYTHONPATH environment variable is not set, so the /opt/app/ directory is not searched.

Answer

The 'common' package itself is already imported and cached, so adding a new module does not become visible.

Question 10

A developer wants to create a class that logs every attribute access on an instance. Which special method should they override?

Accepted Answer

`__getattribute__`. `__getattribute__` is the special method that is called unconditionally for every attribute access on an instance, making it the appropriate choice for logging all attribute accesses. Overriding this method allows the developer to intercept and log each access before the attribute is retrieved, whereas `__getattr__` is only invoked when the attribute is not found via normal lookup.

Answer

`__getattr__`

Answer

`__setattr__`

Answer

`__delattr__`

Question 11

Which THREE of the following are valid ways to create a string in Python?

Accepted Answer

'world'. All five options are valid ways to create a string in Python. 'world' (A) is a single-quoted string literal, str(['h','i']) (B) uses the str() constructor to convert a list into its string representation ''['h', 'i']'', '''multi-line''' (C) is a triple-quoted string literal, str(None) (D) converts the None object into the string 'None', and 'hello' (E) is a double-quoted string literal. The str() function returns a string for any argument, making B and D just as valid as the literals A, C, and E.

Question 12

A Python script uses a third-party library 'requests'. The developer wants to ensure that the exact version 2.25.1 is installed in the project's environment. Which tool and command should be used?

Accepted Answer

pip install requests==2.25.1. Both options B and C are correct because they use the standard pip syntax for pinning a specific version: `package==version`. The command `pip install requests==2.25.1` (B) works on systems where `pip` is linked to Python 3, while `pip3 install requests==2.25.1` (C) explicitly invokes the Python 3 version of pip. Both achieve the same result—installing requests exactly version 2.25.1. Option A fails to specify a version, and option D contains a typo ('instll') that will fail.

Answer

pip install requests

Answer

pip instll requests==2.25.1

Question 13

Which of the following correctly uses `__slots__` to restrict attribute creation to only `x` and `y`?

Accepted Answer

`class Foo: __slots__ = ['x', 'y']`. Options C and D are both correct because `__slots__` must be assigned an iterable of strings. A list `['x', 'y']` and a tuple `('x', 'y')` are both valid iterables that restrict attribute creation to exactly `x` and `y`. Option A uses a single string, which would restrict to individual characters `'x'`; Option B uses a string in parentheses without a trailing comma, which is also just a string. Both A and B would produce unexpected behavior.

Answer

`class Foo: __slots__ = 'x'`

Answer

`class Foo: __slots__ = ('x')`

Question 14

Refer to the exhibit. What happens when the code is executed?

Accepted Answer

A TypeError is raised. The code attempts to modify a string by assigning a new character to an index position (s[0] = 'H'). Strings in Python are immutable, meaning their elements cannot be changed after creation. This operation raises a TypeError because the item assignment is not supported for string objects.

Answer

The string becomes "Hallo"

Answer

A SyntaxError is raised

Answer

The code runs without error and s remains "Hello"

Question 15

Which TWO of the following can be used to remove leading whitespace (spaces, tabs, newlines) from a string? (Choose exactly 2 correct answers.)

Accepted Answer

lstrip(). The `lstrip()` method removes all leading whitespace characters (spaces, tabs, newlines) from the left side of a string. `strip()` removes leading and trailing whitespace, so it also satisfies the requirement of removing leading whitespace. Both are built-in string methods in Python.

Answer

rstrip()

Answer

trim()

Answer

clean()

Question 16

Consider the following code snippet: s = 'abcdefgh'; result = s[7:3:-2]; print(result). What is the output?

Accepted Answer

hf. The slice s[7:3:-2] starts at index 7 (character 'h'), goes backwards with step -2, and stops before index 3. The indices visited are 7 and 5, yielding 'h' and 'f', so the result is 'hf'. Option B is correct because the step is negative, meaning the slice moves from right to left, and the stop index is exclusive.

Answer

fh

Answer

h

Answer

hfd

Question 17

A junior developer writes a class 'Logger' that should only ever have one instance (singleton). They attempt to implement it by overriding __new__ to always return the same instance. However, when multiple threads attempt to create a Logger, they sometimes get different instances. Which modification will make the singleton thread-safe?

Accepted Answer

Use a lock (threading.Lock) in __new__ to serialize access. The race condition occurs when multiple threads simultaneously check `cls._instance` and find it `None`, then both proceed to create a new instance. Wrapping the creation logic inside a `threading.Lock` in `__new__` ensures that only one thread can execute the critical section at a time, guaranteeing that only one instance is ever created.

Answer

Use a class method get_instance() that checks a class variable and creates the instance if needed, and call that from __init__

Answer

Use a metaclass that overrides __call__ to return the singleton

Answer

Override __init__ to check if the instance was already initialized and if so, skip initialization

Question 18

Which THREE of the following are immutable types in Python?

Accepted Answer

str. (str) is correct because strings in Python are immutable sequences of Unicode code points. Once a string object is created, its contents cannot be changed; any operation that appears to modify a string (e.g., concatenation or slicing) actually creates a new string object in memory.

Answer

bytearray

Answer

list

Question 19

A developer defines a class with an __init__ method that sets instance attributes. Which of the following is the correct way to call the parent class's __init__ from a child class?

Accepted Answer

super().__init__(arg1, arg2). `super().__init__(arg1, arg2)` is the modern, recommended way to call the parent class's `__init__` method in Python. It uses the `super()` function without arguments to automatically resolve the parent class based on the method resolution order (MRO), ensuring proper cooperative multiple inheritance and avoiding hardcoding the parent class name.

Answer

super(self, Child).__init__(arg1, arg2)

Answer

Parent.__init__(self, arg1, arg2)

Answer

Child.__init__(self, arg1, arg2)

Question 20

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