PCAP Practice Test 3 — 10 Questions

Question 1

Which of the following is a correct use of the @property decorator to create a getter and setter for an attribute named 'score' that ensures score stays between 0 and 100?

Accepted Answer

@property
def score(self): return self._score
@score.setter
def score(self, value): if 0 <= value <= 100: self._score = value. It uses the @property decorator to define a getter method that returns the private attribute `self._score`, and a setter method that validates the new value is between 0 and 100 before assigning it to `self._score`. This ensures encapsulation and data validation, which is the intended use of properties in Python.

Answer

@property
def _score(self): return self.score
@_score.setter
def _score(self, value): self.score = value

Answer

@property
def score(self): return self.score
@score.setter
def score(self, value): self.score = value

Answer

def get_score(self): return self._score
def set_score(self, value): self._score = value
score = property(get_score, set_score)

Question 2

A developer notices that a custom package 'mypackage' is not being found when importing, even though it is installed in the site-packages directory. The developer suspects a conflict with another package of the same name. Which command should the developer run to diagnose the location from which Python is importing the package?

Accepted Answer

print(mypackage.__file__). `mypackage.__file__` returns the filesystem path from which the module was loaded, allowing the developer to see exactly which `mypackage` Python is using. This directly reveals if the wrong package (e.g., from a different location or a conflicting installation) is being imported instead of the intended one.

Answer

print(mypackage)

Answer

print(__file__)

Answer

import os; print(os.getcwd())

Question 3

Which of the following is the BEST practice for building a large string by concatenating many smaller strings in Python?

Accepted Answer

result = ''.join(parts). `''.join(parts)` is the most efficient way to concatenate a large number of strings in Python. It allocates memory once for the final string by iterating over the list and copying each part into the result buffer, avoiding the O(n²) time complexity of repeated concatenation in a loop.

Answer

result = sum(parts, '')

Answer

result = str.concat(*parts)

Answer

result = ''; for part in parts: result += part

Question 4

A developer has two separate directories on sys.path: /home/user/libs and /opt/libs. Both directories contain a subdirectory 'mypackage' without an __init__.py file. The developer wants to import a module from 'mypackage' that exists only in one of the directories. What concept allows Python to treat these two directories as a single namespace package?

Accepted Answer

Implicit namespace packages (PEP 420). PEP 420 introduced implicit namespace packages, which allow multiple directories on sys.path to contribute to the same package without requiring __init__.py files. When Python encounters a directory without __init__.py, it treats it as a namespace package, merging all matching directories across sys.path into a single logical package. This enables the developer to import a module from 'mypackage' that exists in only one of the directories, as Python searches all paths and resolves the module from the first location where it is found.

Answer

Regular packages with __init__.py

Answer

sys.path merging

Answer

Package overriding

Question 5

Which TWO of the following statements about Python's `sys.path` are true?

Accepted Answer

Module search stops at the first matching directory in `sys.path`.. Python's import mechanism iterates through `sys.path` in order and stops at the first directory containing the requested module. Option E is correct: the directory containing the script (or the current directory when running interactively) is inserted at the beginning of `sys.path` at startup. Options A, C, and D are false: the current working directory is not always first (the script's directory takes precedence), `sys.path` is initialized from the `PYTHONPATH` environment variable *in addition to* default paths, and `sys.path` is a list, not a tuple. Therefore, only two statements are true.

Answer

The current working directory is always the first element in `sys.path`.

Answer

`sys.path` is initialized from the PYTHONPATH environment variable.

Answer

`sys.path` is a tuple of strings.

Question 6

What is the result of the expression '12345'[:10]?

Accepted Answer

'12345'. In Python, slicing a string with a start index of 0 and an end index of 10 (as in '12345'[:10]) returns the entire string if the slice end exceeds the string length. Since '12345' has only 5 characters, the slice extracts all characters without padding or error, resulting in '12345'.

Answer

'12345     '

Answer

IndexError

Answer

'12345 '

Question 7

A user wants to ensure that a custom module 'mymod' located at '/home/user/custom' takes precedence over a standard library module with the same name. Which operation on sys.path should be performed?

Accepted Answer

sys.path.insert(0, '/home/user/custom'). `sys.path.insert(0, '/home/user/custom')` adds the custom module's directory to the very beginning of the module search path. Python's import system scans `sys.path` in order, so placing the custom directory first ensures that `mymod` is found there before any standard library or site-packages directory that might contain a module with the same name.

Answer

sys.path.replace('/', '/home/user/custom')

Answer

sys.path.append('/home/user/custom')

Answer

sys.prefix = '/home/user/custom'

Question 8

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.. Every Python class has an `__mro__` attribute that returns a tuple of classes in the order they are searched for methods and attributes. This attribute is automatically generated by the C3 linearization algorithm and provides a clear, inspectable view of the resolution order.

Answer

The MRO is only used for methods, not attributes.

Answer

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

Question 9

A Python class 'BankAccount' has a method 'withdraw(amount)' that deducts 'amount' from 'self.balance'. A developer writes a subclass 'SavingsAccount' that overrides 'withdraw' to add a penalty if balance drops below minimum. Which design pattern is being used?

Accepted Answer

Method overriding. Method overriding is the mechanism where a subclass provides a specific implementation of a method that is already defined in its superclass. In this scenario, SavingsAccount overrides the withdraw method from BankAccount to add penalty logic, which is the defining characteristic of method overriding in Python.

Answer

Composition

Answer

Aggregation

Answer

Inheritance

Question 10

A developer is writing a package that contains multiple modules. The package should allow users to import it directly and have all commonly used functions available at the package level. For example, after `import mypackage`, the user should be able to call `mypackage.func1()` without needing to import submodules. Which is the best way to achieve this?

Accepted Answer

In `__init__.py`, import the desired functions from the submodules, e.g., `from .submodule import func1`.. `__init__.py` is executed when a package is imported, and importing functions from submodules into `__init__.py` makes them directly accessible as attributes of the package object. This allows `mypackage.func1()` to work without requiring the user to import submodules explicitly, satisfying the requirement of a flat namespace at the package level.

Answer

Create a wrapper function in `__init__.py` that delegates calls to the submodule functions.

Answer

Include `__all__` in each submodule and ensure `__init__.py` is empty.

Answer

Define a list named `__all__` in the package's `__init__.py` that lists the functions.