PCAP Practice Test 17 — 15 Questions

Question 1

A user runs script.py and gets the above error: ModuleNotFoundError: No module named 'mypackage'. Which of the following is the most likely cause?

Accepted Answer

The package mypackage is not installed or not in the Python path.. The error message 'ModuleNotFoundError: No module named 'mypackage'' indicates that Python cannot find the module 'mypackage'. This typically occurs when the package is not installed or not present in sys.path. Option C directly addresses this cause. The other options are less plausible: Option A would raise an AttributeError, not a ModuleNotFoundError; Option B might cause import issues but would likely result in a circular import error or import error due to naming conflicts; Option D's syntax error would prevent the script from running at all. Therefore, Option C is the most probable cause.

Answer

The function myfunction does not exist in mypackage.

Answer

The script.py is inside the mypackage directory, causing a conflict.

Answer

There is a syntax error in script.py.

Question 2

Which TWO methods are valid ways to import a function named 'foo' from a module 'bar' that is part of a package 'pkg'?

Accepted Answer

from pkg.bar import foo. The 'from pkg.bar import foo' syntax directly imports the 'foo' function from the 'bar' submodule within the 'pkg' package, making 'foo' available in the current namespace. Option D is also correct because it first imports the 'bar' module from 'pkg' using 'from pkg import bar', then accesses 'foo' as an attribute of 'bar' (bar.foo), which is a valid two-step approach.

Answer

import bar

Answer

import pkg; pkg.bar.foo

Answer

import pkg.bar.foo

Question 3

A programmer wants to check whether a string `s` is a palindrome (reads the same forwards and backwards, ignoring case and non-alphanumeric characters). Which code snippet correctly implements this?

Accepted Answer

clean = ''.join(c for c in s if c.isalnum()); return clean.lower() == clean.lower()[::-1]. It first filters out non-alphanumeric characters using `c.isalnum()`, then converts the cleaned string to lowercase before comparing it with its reverse via slicing `[::-1]`. This ensures that case differences and punctuation/spaces are ignored, which is required for a proper palindrome check per the problem statement.

Answer

s.lower() == s.lower()[::-1]

Answer

s == s[::-1]

Answer

return s.lower() == ''.join(reversed(s.lower()))

Question 4

A developer has a function that performs several operations and may raise different exceptions. The developer wants to catch a specific exception and then re-raise it after logging. Which code snippet correctly re-raises the same exception without losing its traceback?

Accepted Answer

except ValueError as e: log.error(e); raise. Using a bare `raise` statement inside an `except` block re-raises the original exception instance, preserving its full traceback. This is the standard Python idiom for logging an exception and then propagating it unchanged, ensuring that the original call stack and error context are not lost.

Answer

except ValueError as e: log.error(e); return None

Answer

except ValueError as e: log.error(e); raise ValueError('New')

Answer

except ValueError as e: log.error(e); pass

Question 5

Which of the following is the correct way to open a file for writing in text mode, ensuring that if the file already exists it will be overwritten?

Accepted Answer

open('file.txt', 'w'). The 'w' mode opens the file for writing in text mode and truncates the file to zero length if it exists, or creates a new file if it does not. This ensures any existing content is overwritten, which matches the requirement.

Answer

open('file.txt', 'x')

Answer

open('file.txt', 'r+')

Answer

open('file.txt', 'a')

Question 6

A developer wants to use a function 'calculate' from a module 'math_ops' that is located in a sibling directory '../shared/' relative to the current script. What is the correct way to import it using an absolute import assuming the shared directory is a package with __init__.py and the project root is in sys.path?

Accepted Answer

from shared.math_ops import calculate. Absolute imports in Python use the project root as the base, not relative paths. Since the project root is in sys.path, 'from shared.math_ops import calculate' directly references the 'shared' package at the top level, regardless of the current script's location. This is the standard absolute import syntax as defined in PEP 328.

Answer

from .shared.math_ops import calculate

Answer

from ..shared.math_ops import calculate

Answer

import ..shared.math_ops

Question 7

When processing a large text file, a developer notices that using str.replace() in a loop is slow. Which alternative is most efficient for multiple replacements?

Accepted Answer

Use str.translate() with a translation table. `str.translate()` with a translation table built by `str.maketrans()` performs all character replacements in a single pass over the string, operating at the C level in CPython. This avoids the O(n) per-replacement overhead of `str.replace()` in a loop, making it the most efficient choice for multiple, fixed-character substitutions on large text.

Answer

Use str.maketrans() on the original string

Answer

Use re.sub() from the re module

Answer

Chain multiple str.replace() calls

Question 8

A developer needs to write a function that safely divides two numbers and returns None if division by zero occurs. Which implementation is most Pythonic?

Accepted Answer

def safe_divide(a, b):
    try:
        return a/b
    except ZeroDivisionError:
        return None. It uses a try-except block to catch the specific ZeroDivisionError that Python raises when dividing by zero. This is the most Pythonic approach, following the EAFP (Easier to Ask for Forgiveness than Permission) principle, which is preferred over LBYL (Look Before You Leap) in Python. The function returns None only when the exception occurs, preserving the natural behavior of division for all other cases.

Answer

def safe_divide(a, b):
    return a/b if b else None

Answer

def safe_divide(a, b):
    if b != 0:
        return a/b
    else:
        return None

Answer

def safe_divide(a, b):
    try:
        return a/b
    except ValueError:
        return None

Question 9

A programmer writes a class with a static method using @staticmethod. What is the primary purpose of using a static method instead of a class method or instance method?

Accepted Answer

To define a method that does not depend on class or instance state and behaves like a regular function but is namespaced inside the class. A static method in Python, decorated with @staticmethod, does not receive an implicit first argument (neither self nor cls). This means it cannot access or modify class or instance state; it behaves exactly like a regular function but is organized within the class's namespace for logical grouping. The primary purpose is to encapsulate utility functions that are related to the class but do not depend on its data.

Answer

To access class variables without creating an instance

Answer

To allow the method to be overridden in subclasses

Answer

To enforce that the method cannot be called from an instance

Question 10

A class has an attribute that should be computed on access and cached for subsequent accesses. Which pattern is most appropriate?

Accepted Answer

Use a custom descriptor that caches the value in the instance's __dict__.. A custom descriptor with a __get__ method can compute the attribute value on first access and store it in the instance's __dict__ for subsequent accesses. This pattern, often called a cached property, ensures the computation happens only once per instance, which is exactly what the question requires.

Answer

Use __slots__ to define the attribute.

Answer

Use a @classmethod to compute the value.

Answer

Use a @staticmethod to compute the value.

Question 11

A developer writes a function that reads a configuration file and returns its contents as a string. The file might not exist. Which exception should be caught to handle a missing file?

Accepted Answer

FileNotFoundError. `FileNotFoundError` is a built-in exception in Python that is raised when a file or directory is requested but does not exist. In Python 3, file-related I/O errors are organized under `OSError` with specific subclasses, and `FileNotFoundError` is the precise exception for a missing file, making it the most appropriate catch for this scenario.

Answer

PermissionError

Answer

IOError

Answer

OSError

Question 12

A small web application allows users to download files from a server. The code uses open() without any exception handling. When a user requests a non-existent file, the server crashes with a traceback and returns a 500 Internal Server Error to the client. The team needs to modify the code to handle this situation gracefully: if the file does not exist, the application should return a 404 Not Found response (by calling a function send_404()). The application should not catch unrelated exceptions like KeyboardInterrupt. Which modification is the most appropriate?

Accepted Answer

Wrap the open() call in a try-except block catching FileNotFoundError, and in the except block call send_404().. It catches the specific exception raised when a file is not found (FileNotFoundError), which is a subclass of OSError. This allows the code to return a 404 response for missing files while not catching unrelated exceptions like KeyboardInterrupt, as required. The except block calls send_404() to handle the missing file gracefully without crashing the server.

Answer

Wrap the entire request handling in a try-except block catching Exception, and if any exception occurs, call send_500().

Answer

Check if the file exists using os.path.exists before opening, and if not, call send_404().

Answer

Wrap the open() call in a try-except block catching OSError, and in the except block call send_404().

Question 13

Which TWO string methods raise an exception when the searched substring is not found?

Accepted Answer

rindex(). (rindex()) is correct because the rindex() method, like index(), raises a ValueError exception when the searched substring is not found. This is in contrast to rfind() and find(), which return -1 instead of raising an exception.

Answer

rfind()

Answer

find()

Answer

count()

Question 14

A developer is working on a project that requires the use of a third-party package hosted on a private repository. The developer wants to ensure that the package can be imported without specifying the full repository URL each time. Which approach should be taken?

Accepted Answer

Configure the repository URL in pip's configuration file or in requirements.txt.. Configuring the repository URL in pip's configuration file (e.g., `pip.conf`, `pip.ini`, or `~/.config/pip/pip.conf`) or in `requirements.txt` using the `--index-url` or `--extra-index-url` option allows pip to resolve the package from the private repository automatically. This approach ensures that the package can be installed and imported without manually specifying the full URL each time, as pip will use the configured index to locate and download the package.

Answer

Append the repository path to sys.path in the script.

Answer

Place the package files in the site-packages directory manually.

Answer

Use os.system to run a pip install command from within the script.

Question 15

Which of the following best describes the use of the @abstractmethod decorator in Python?

Accepted Answer

It indicates that a method must be overridden in any non-abstract subclass.. The @abstractmethod decorator, when used in conjunction with a metaclass like ABC (Abstract Base Class) or by inheriting from ABC, declares a method as abstract. This forces any concrete (non-abstract) subclass to provide an override of that method; otherwise, Python raises a TypeError at instantiation time. Option B correctly captures this mandatory override requirement.

Answer

It automatically provides a default implementation for a method.

Answer

It creates a method that can be called without an instance.

Answer

It raises AttributeError if the method is called.