PCAP Practice Test 24 — 15 Questions

Question 1

A developer is designing a class hierarchy for a library system. They want to ensure that a method 'borrow' in the base class 'Item' can be overridden by subclasses like 'Book' and 'DVD', but the base implementation should not be callable directly. Which approach best achieves this?

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

Accepted Answer

Define borrow with raise NotImplementedError and override in subclasses. Raising `NotImplementedError` in the base class `Item.borrow` makes the method abstract in practice: it cannot be called directly without causing an error, forcing subclasses like `Book` and `DVD` to provide their own override. This pattern enforces that the base implementation is never invoked accidentally, while still allowing polymorphic dispatch through inheritance.

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Define borrow as a static method and override in subclasses

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Define borrow as a class method and override in subclasses

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Define borrow with pass and let subclasses override

Question 2

A developer generates a report where numbers must be right-aligned in a 10-character column using f-strings: f'{value:>10}'. However, some values may be None, causing a TypeError. Which is the most robust way to handle None values without affecting other falsy values like 0?

Accepted Answer

f'{value if value is not None else "N/A":>10}'. It uses an explicit identity check (`value is not None`) to distinguish `None` from other falsy values like `0` or empty strings. This ensures that `0` is still right-aligned as a number, while `None` is replaced with the string `"N/A"` before formatting. The f-string then applies the `>10` alignment specifier to the resulting value.

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Use str.format() with a conditional for the format spec

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f'{value or "N/A":>10}'

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Wrap the f-string in a try-except block

Question 3

Which of the following statements about the __init__.py file in a package is true?

Accepted Answer

It is required for a directory to be considered a regular package. In Python, a directory containing an `__init__.py` file is recognized as a regular package. This file can be empty or contain initialization code, and its presence is required for the directory to be imported as a package (as opposed to a namespace package). Without it, Python will not treat the directory as a regular package.

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It is required for a namespace package

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It cannot contain executable code

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It is automatically generated by Python

Question 4

A developer creates a package named 'mypkg' with an __init__.py file. Inside the package, there is a module 'utils.py'. Which of the following is the correct way to import the function 'helper' from 'utils' from outside the package?

Accepted Answer

from mypkg.utils import helper. It uses the standard Python syntax for importing a specific name from a submodule within a package: `from package.module import name`. This directly imports the `helper` function into the current namespace, making it callable without any prefix. The `__init__.py` file marks `mypkg` as a package, and `utils.py` is a module inside it, so `from mypkg.utils import helper` is the proper way to access `helper` from outside the package.

Answer

import mypkg.utils.helper

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import mypkg; mypkg.utils.helper

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from mypkg import utils.helper

Question 5

Match each code snippet to its output.

Accepted Answer

2 + 3 * 4: 14. Understand operator precedence: exponentiation > multiplication/division > addition/subtraction. Parentheses override precedence. Integer division (//) returns floor division quotient, while modulo (%) returns remainder.

Answer

2 ** 3: 6

Answer

10 // 3: 1

Question 6

Refer to the exhibit. What is the effect of using 'from None' in the raise statement?

Accepted Answer

It suppresses the exception chain and only shows the TypeError. In Python, 'raise TypeError(...) from None' explicitly suppresses the exception context, so the traceback shows only the TypeError and hides the original ValueError that triggered it. This is used when the original exception is irrelevant or confusing to the caller. Without 'from None', Python would chain the exceptions and display both.

Answer

It re-raises the original ValueError

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It causes a syntax error

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It chains the TypeError to the original ValueError

Question 7

A Python script that processes log files uses the following code:
    with open('log.txt', 'r') as f:
        lines = f.readlines()
    for line in lines:
        # process
What is a potential inefficiency in this code?

Accepted Answer

Reading the entire file into memory may be wasteful for large files.. `readlines()` loads the entire file into memory as a list of strings. For large log files, this can consume significant memory and cause performance degradation or even memory errors. A more memory-efficient approach is to iterate directly over the file object (e.g., `for line in f:`), which reads one line at a time from disk.

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The file is not properly closed after processing.

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Using readlines() is the most efficient way to iterate over lines.

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The file should be opened in binary mode for better performance.

Question 8

A class defines an __init__ method that takes optional arguments. What is the correct way to provide default values?

Accepted Answer

Use default parameter values in the __init__ signature.. Python's `__init__` method, like any other function, supports default parameter values in its signature. This is the idiomatic and simplest way to provide default values for instance attributes, as the defaults are evaluated at function definition time and assigned to the parameter when no argument is provided.

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Use class variables to store defaults.

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Override __new__ to set default values.

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Use a separate setter method called after instantiation.

Question 9

Which TWO of the following statements about Python classes are true? (Select exactly 2.)

Accepted Answer

Class variables are shared among all instances.. Class variables are defined directly in the class body and are shared across all instances of that class. When you modify a class variable through the class itself, the change is reflected in every instance, as the variable is stored in the class's __dict__ rather than in each instance's __dict__.

Answer

Class names should be written in snake_case per PEP 8.

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Private attributes (starting with __) cannot be accessed outside the class.

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__init__ is the constructor of a class.

Question 10

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

Accepted Answer

'Hello'. In Python, valid string literals can be enclosed in single quotes, double quotes, triple single quotes, or triple double quotes. Formatted string literals (f-strings) are also valid. Option A is invalid because it uses mismatched quote characters: it opens with a single quote but closes with a double quote. Option B uses consistent single quotes. Option C is an f-string. Option D uses backticks, which are not valid Python string delimiters. Option E uses triple single quotes, which are valid for multi-line strings.

Answer

'Hello"

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`Hello`

Question 11

What is the result of 'abcdef'[::-2]?

Accepted Answer

'fdb'. The slicing syntax [::-2] means start from the end (default step negative), go to the beginning, and take every second character in reverse order. For 'abcdef', starting at 'f' (index -1), then skipping one to 'd' (index -3), then 'b' (index -5), resulting in 'fdb'. Option C is correct.

Answer

'dfb'

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'ace'

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'eca'

Question 12

A developer wants to remove all leading and trailing whitespace from a string, but preserve internal spaces. Which line of code accomplishes this?

Accepted Answer

s = s.strip(). `s.strip()` removes all leading and trailing whitespace characters (spaces, tabs, newlines) from the string while preserving internal spaces. This is the exact requirement: eliminate whitespace at the boundaries only, leaving the internal content unchanged.

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s = s.lstrip()

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s = s.strip().lstrip()

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s = s.replace(' ', '')

Question 13

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)

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print('abc')

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float('abc')

Question 14

Which three statements about the Method Resolution Order (MRO) in Python are true? (Choose three.)

Accepted Answer

The MRO can be viewed using the __mro__ attribute.. Option A is correct because Python exposes the computed MRO as a tuple through the __mro__ attribute on every class (and also via ClassName.mro()), so it can be inspected directly. Option B is correct because since Python 2.3 the MRO is computed using the C3 linearization algorithm, which guarantees a consistent, monotonic ordering that respects local precedence and the order of base classes. Option D is correct because in a diamond hierarchy C3 linearization places the most derived class first and the common topmost base class (e.g., object) last, after all intermediate classes. Option C is not correct because the MRO governs attribute lookup in general, including non-method attributes such as data descriptors and class variables, not just methods. Option E is not correct because the MRO is computed once when the class is created and is stored in the class's __mro__; altering the class hierarchy at runtime does not recompute or allow modification of an existing class's MRO.

Answer

The MRO is only used for methods, not attributes.

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The MRO can be changed by modifying the class hierarchy at runtime.

Question 15

A developer wants to convert a string 'Python' to all uppercase letters. Which string method should be used?

Accepted Answer

upper(). The `upper()` method returns a copy of the string with all lowercase characters converted to uppercase. Since the goal is to convert 'Python' to 'PYTHON', `upper()` is the correct and most direct method for this task.

Answer

capitalize()

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title()

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swapcase()