PCAP Practice Test 4 — 10 Questions

Question 1

Given that MyClass defines __private_attr in __init__, why does this error occur?

Accepted Answer

The attribute name is mangled to _MyClass__private_attr.. Python uses name mangling for attributes with double underscores (__) to avoid accidental overriding in subclasses. When you define __private_attr inside __init__, Python internally renames it to _MyClass__private_attr. Attempting to access obj.__private_attr from outside the class fails because that mangled name is not recognized, leading to an AttributeError.

Answer

The attribute was not defined in __init__.

Answer

Private attributes cannot be accessed outside the class.

Answer

The attribute is a class attribute not an instance attribute.

Question 2

Your company has two separate Python packages: 'app' and 'lib'. They are maintained by different teams. 'app' depends on 'lib', but 'lib' is still under development and its API changes frequently. To avoid breaking 'app', the team decides to use a virtual environment and install a specific version of 'lib'. However, during development, they need to test 'app' with the latest 'lib' changes from the Git repository. The current workflow is: (1) activate virtual env, (2) install 'lib' from local source using `pip install -e /path/to/lib`. This installs 'lib' as a development package. But one developer reports that after pulling latest 'lib' changes, importing 'lib' in 'app' still uses the old version even after re-running pip install -e. What is the most likely reason?

Accepted Answer

The editable install may still point to an old copy of the library if the source directory was moved or if there is a stray .egg-link file.. The most likely reason is D. When using `pip install -e` (editable install), pip creates a special `.egg-link` file (or similar pointer) in the site-packages directory that points to the source directory. If the source directory was moved, renamed, or if a stale `.egg-link` file remains from a previous install, pip may still reference the old location, causing the old version to be imported even after re-running the install command. This is a known subtlety of editable installs, especially when the source code is managed under version control and the directory structure changes.

Answer

Python caches imported modules in sys.modules, so importing again does not reload the module from disk.

Answer

The package 'lib' is being imported as a namespace package, so changes are not picked up.

Answer

The .pyc files are not being invalidated because the timestamps are not updated.

Question 3

You are developing a package 'analytics' that contains subpackages 'stats' and 'ml'. The __init__.py of 'analytics' imports a function 'normalize' from 'analytics.stats'. When a user runs `import analytics`, they get an ImportError. Which change ensures the package imports correctly?

Accepted Answer

Change the import in analytics/__init__.py to: from .stats import normalize. It uses an explicit relative import (`from .stats import normalize`), which is the proper way to import from a subpackage within a package. Absolute imports like `from analytics.stats import normalize` can fail if the package's parent directory is not in `sys.path`, which is common when running scripts directly. Relative imports resolve correctly based on the package structure, ensuring the import works regardless of how the package is invoked.

Answer

Change the import to: from stats import normalize

Answer

Add sys.path.append('.') before the import in __init__.py

Answer

Move the import statement to the stats/__init__.py file

Question 4

A programmer writes a function that expects a string and returns it reversed. Which code snippet correctly reverses the string 'stressed' to 'desserts'?

Accepted Answer

result = s[::-1]. Both option B and option D correctly reverse the string 'stressed' to 'desserts'. Option B uses slice notation `[::-1]`, which creates a reversed copy of the string by stepping from end to start with a step of -1. This is the most direct and idiomatic way to reverse a string in Python. Option D uses `''.join(reversed(s))`: `reversed(s)` returns an iterator that yields characters in reverse order, and `join()` concatenates them into a new string. This is also a valid and correct approach. Option A is incorrect because strings do not have a `reversed()` method; `reversed()` is a built-in function. Option C is incorrect because `.reverse()` is a list method, not a string method, and strings are immutable.

Answer

result = s.reversed()

Answer

s.reverse()

Question 5

Refer to the exhibit. What is the output?

Accepted Answer

1 2. '1 2'. When `print(A.x, a.x)` is executed, `A.x` accesses the class attribute `x=1`, and `a.x` accesses the instance attribute `x=2` (set in `__init__`), which shadows the class attribute for that instance. Therefore, the output is '1 2'.

Answer

1 1

Answer

0 1

Answer

2 2

Question 6

Refer to the exhibit. A developer ran the script and saw the above traceback. The intended behavior was to load a JSON configuration file, and if the file is missing, create a default config. What is the most likely root cause of the second exception (NameError)?

Accepted Answer

The script did not import the json module.. The traceback shows a NameError for 'json.loads', which indicates that the name 'json' is not defined in the current namespace. This occurs when the script attempts to call json.loads() without first importing the json module. The intended behavior of loading a JSON configuration file requires the json module to parse the file content, and its absence causes the NameError exception.

Answer

The variable 'f' was not defined due to the FileNotFoundError.

Answer

The config.json file exists but is empty.

Answer

The file was opened in binary mode instead of text mode.

Question 7

Refer to the exhibit. What is the output?

Accepted Answer

100. The code `print('100')` outputs the string `100` without quotes. In Python, `print()` displays the value passed to it; when a string literal is passed, it prints the characters of the string, not the surrounding quotes. Therefore, the output is `100` (the integer-like string, but as a string). Option B is correct because it shows the numeric value without quotes, which is how Python's `print()` renders a string.

Answer

'100'

Answer

True

Answer

Error

Question 8

Consider a class `D` that inherits from multiple base classes `B` and `C`. The developer wants to call a method from a specific parent class while ensuring correct method resolution order (MRO). Which is the safest way?

Accepted Answer

`super().method()`. In Python, `super().method()` is the safest way to call a method from a parent class in a multiple inheritance scenario because it respects the Method Resolution Order (MRO) defined by the C3 linearization algorithm. This ensures that the method is resolved from the next class in the MRO, avoiding hard-coded references that could break if the inheritance hierarchy changes. It also correctly handles cooperative multiple inheritance, where each class in the MRO can collaborate via `super()` calls.

Answer

`self.method()`

Answer

`ParentClass.method(self)`

Answer

`BaseClass.method(self)`

Question 9

A developer installs a third-party package using pip, but when they try to import it in their script, Python raises a ModuleNotFoundError. The package is definitely installed (pip list shows it). What is the most likely cause?

Accepted Answer

The Python interpreter being used is different from the one where the package was installed.. When a package is installed via pip, it is placed into the site-packages directory of a specific Python interpreter. If the developer runs their script with a different Python interpreter (e.g., one from a virtual environment, a different version, or a system Python vs. a user-installed Python), that interpreter's import system will not search the site-packages where the package was installed, resulting in a ModuleNotFoundError even though pip list shows the package. This is the most common cause of such a mismatch.

Answer

The package name contains a hyphen.

Answer

The script is in a directory that shadows the package name.

Answer

The package does not have an __init__.py file.

Question 10

A developer is creating a custom exception hierarchy for a library. The base exception is `LibraryError`. Which definition ensures that subclasses can be caught using the parent exception, but also allows distinguishing between different error types?

Accepted Answer

class LibraryError(Exception): pass
class FileError(LibraryError): pass
class ParseError(LibraryError): pass. It defines `LibraryError` as a subclass of `Exception`, which is the proper base class for all user-defined exceptions in Python. Subclasses `FileError` and `ParseError` inherit from `LibraryError`, so they can be caught with `except LibraryError` while still being distinguishable by their own type. This follows the standard Python exception hierarchy, where custom exceptions should derive from `Exception`, not `BaseException` or no base class.

Answer

class LibraryError: pass
class FileError(LibraryError): pass
class ParseError(LibraryError): pass

Answer

class LibraryError(BaseException): pass
class FileError(LibraryError): pass
class ParseError(LibraryError): pass

Answer

class LibraryError(Exception): pass
class FileError(Exception): pass
class ParseError(Exception): pass