PCAP Practice Test 15 — 15 Questions

Question 1

You are a developer for a data science team. The team uses a shared module 'utilities' located at /team/shared/utilities.py. This module is not part of any package, and they want to import it from various project scripts without copying the file. Some projects are in /home/user/proj_A/ and others in /var/data/proj_B/. Currently, each script manually adds /team/shared/ to sys.path using sys.path.insert(0, '/team/shared/'). This works but is repetitive. The team wants a cleaner solution that also works when the script is run from different working directories. They consider creating a package 'utilities' by adding an __init__.py to the directory and using relative imports. However, the module currently uses absolute imports for some external libraries. What is the best course of action to allow clean imports of utilities from any location while minimizing changes to the module itself?

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

Accepted Answer

Set the PYTHONPATH environment variable to include /team/shared/ in the shell profile.. Setting the PYTHONPATH environment variable to include /team/shared/ is the best solution because it automatically adds that directory to the module search path for all Python scripts without modifying the module itself or requiring repetitive code. This approach works regardless of the current working directory and preserves the module's existing absolute imports. Other options either do not add the directory to the search path, require modifying the module, or are more complex to implement.

Answer

Create an empty __init__.py in /team/shared/ to make it a namespace package.

Answer

Place a .pth file in the site-packages directory that points to /team/shared/.

Answer

Convert utilities.py into a package by adding __init__.py and using relative imports inside.

Question 2

You are developing a high-performance logging module that must handle thousands of log entries per second. Each entry is built by concatenating a timestamp, level, and message. Currently, your code uses a loop that repeatedly appends to a string using the += operator. This results in high memory usage and sluggish performance because each concatenation creates a new string object. The module must run on systems with limited memory and cannot rely on external libraries. Which course of action would best resolve the performance issue while maintaining readability and standard library compliance?

Accepted Answer

Collect the string parts in a list and use str.join() to combine them at the end.. Collecting string parts in a list and using str.join() avoids repeated string concatenation, which creates a new string object for each += operation. This approach reduces memory allocation overhead and improves performance, especially under high throughput, while remaining fully compliant with standard library constraints.

Answer

Use string formatting (f-strings or format) within the loop to build the log entry.

Answer

Write the log entries directly to a file using file.write() in the loop.

Answer

Continue using += but preallocate a large string buffer using array.array or io.StringIO to reduce reallocation.

Question 3

Which of the following is the correct way to format a string to include a variable value with two decimal places in Python?

Accepted Answer

f"{value:.2f}". Uses the correct f-string format specifier `:.2f`, where `f` stands for fixed-point notation and `.2` specifies two decimal places. This is the standard Python syntax for formatting a floating-point number to two decimal places within an f-string.

Answer

f"{value:.2}"

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f"{value%:.2f}"

Answer

f"{value:2f}"

Question 4

Which THREE of the following are true about the __pycache__ directory?

Accepted Answer

It is automatically created when a module is imported.. Python automatically creates the __pycache__ directory when a module is imported for the first time. This directory stores compiled bytecode files (.pyc) that allow Python to skip recompilation on subsequent imports, thereby improving startup time for later runs.

Answer

It is only created when the script is compiled with -O.

Answer

It should be added to version control.

Question 5

Which TWO statements about the 'from package import *' statement are correct?

Accepted Answer

If __all__ is defined in __init__.py, only the names in __all__ are imported.. When `__all__` is defined in a package's `__init__.py`, the `from package import *` statement imports only the names listed in that `__all__` list. This is the explicit mechanism Python provides to control the public API of a package when using the wildcard import syntax.

Answer

It imports the package itself as a module.

Answer

Without __all__, it imports all public names from the package's __init__.py and all submodules.

Answer

It imports all submodules of the package by default.

Question 6

A Python project uses namespace packages spread across multiple directories. The package structure is: project/ and lib/ both contain subdirectories 'mypkg/'. Each has an __init__.py file. When importing 'mypkg', which directory's contents are used?

Accepted Answer

Only the directory that appears first in sys.path is used.. When both directories contain an __init__.py file, they are regular packages, not namespace packages. Python's import system uses the first match in sys.path; it does not merge regular packages. Therefore, only the directory that appears first in sys.path is used, making option B correct.

Answer

Both directories are merged into a single namespace package.

Answer

An error is raised due to ambiguous import.

Answer

The last directory in sys.path overrides the previous.

Question 7

A developer designs a plugin system where each plugin must implement a method 'execute'. Which code snippet correctly enforces that subclasses provide an implementation using the 'abc' module?

Accepted Answer

from abc import ABC, abstractmethod
class Plugin(ABC): @abstractmethod
def execute(self): pass. It uses both `ABC` as the metaclass and `@abstractmethod` decorator to enforce that subclasses must override the `execute` method. Without `ABC`, the `@abstractmethod` decorator has no effect; without `@abstractmethod`, the method is just a regular method that can be inherited without being overridden. This combination ensures that any concrete subclass that does not implement `execute` will raise a `TypeError` at instantiation time.

Answer

from abc import abstractmethod
class Plugin: @abstractmethod
def execute(self): pass

Answer

from abc import ABC
class Plugin(ABC): def execute(self): pass

Answer

class Plugin: def execute(self): raise NotImplementedError

Question 8

A beginner programmer writes: name = "Alice"; print("Hello " + name). Which string method alternative is more efficient and recommended for Python 3?

Accepted Answer

print(f"Hello {name}"). F-strings (formatted string literals) are the most efficient and readable string formatting method introduced in Python 3.6. They evaluate expressions at runtime and directly interpolate variables into the string, avoiding the overhead of method calls or the older %-formatting, making them both faster and more Pythonic.

Answer

print("Hello {}".format(name))

Answer

print("Hello %s" % name)

Answer

print("Hello " + name) is fine

Question 9

What does the expression 'hello world'.title() return?

Accepted Answer

'Hello World'. The `title()` method in Python returns a copy of the string where the first character of each word is converted to uppercase and all remaining characters are converted to lowercase. For the string 'hello world', this results in 'Hello World', making option A correct.

Answer

'HELLO WORLD'

Answer

'Hello world'

Answer

'hello World'

Question 10

A developer is creating a Python package named 'utils' and wants to control what is imported when a user writes 'from utils import *'. Which file and variable should be defined?

Accepted Answer

Define __all__ = ['mod1', 'mod2'] in '__init__.py' of the 'utils' package.. In Python, the `__all__` variable in the `__init__.py` file of a package explicitly defines the list of module names that are exported when a user writes `from utils import *`. This controls the public API of the package and prevents unintended internal modules from being imported.

Answer

Define __all__ as a function that returns the list of modules in '__init__.py'.

Answer

Set the __all__ variable in the script that imports the package.

Answer

Define __all__ as a list of module objects in the main module 'utils.py'.

Question 11

A developer is designing a system where a `Car` class needs to reuse functionality from `Engine` and `Transmission` without creating a deep hierarchy. Which OOP principle should be applied?

Accepted Answer

Composition over inheritance.. 'Composition over inheritance,' is correct because it advocates building the Car class by composing it with Engine and Transmission objects (has-a relationships) rather than inheriting from them. This avoids a deep class hierarchy and provides flexibility to change or swap components at runtime, which is a key design principle in Python and OOP.

Answer

Aggregation, where Car is part of Engine.

Answer

Singleton pattern for Engine.

Answer

Multiple inheritance to inherit from both.

Question 12

A developer is writing a script that processes user-uploaded CSV files. The script should attempt to read the file, and if a UnicodeDecodeError occurs, log a warning and skip the file. Which code snippet correctly achieves this without stopping the entire process?

Accepted Answer

try: read_file() except UnicodeDecodeError: log.warning('Skipping file'). It catches only UnicodeDecodeError, which is the specific exception raised when a file contains invalid UTF-8 or other encoding issues. It logs a warning and then continues execution (the 'pass' is implied by the log statement, but the key is that the exception is handled without re-raising). This matches the requirement to skip the file without stopping the entire process.

Answer

try: read_file() except (UnicodeDecodeError, OSError): pass

Answer

try: read_file() except Exception: log.warning('Skipping file')

Answer

try: read_file() except UnicodeEncodeError: log.warning('Skipping file')

Question 13

A class defines a variable `count = 0`. An instance modifies `self.count = 5`. What is the value of `count` in the class namespace?

Accepted Answer

0, because the class variable remains unchanged.. When an instance assigns `self.count = 5`, Python creates an instance attribute that shadows the class variable `count` in the instance's namespace. The class variable `count` remains unchanged at 0 in the class namespace, as instance attribute assignment does not modify class attributes.

Answer

5, because the instance modified the class variable.

Answer

0, but the assignment raises an AttributeError.

Answer

The class variable is deleted and the instance has 5.

Question 14

A developer wants to import a specific function 'calculate' from a module named 'formulas' without importing the entire module. Which import statement should be used?

Accepted Answer

from formulas import calculate. The `from module import name` syntax in Python allows you to import a specific function (or other attribute) from a module directly into the current namespace, without importing the entire module. This avoids unnecessary memory usage and keeps the namespace clean by only bringing in the needed `calculate` function.

Answer

import formulas

Answer

import calculate from formulas

Answer

import formulas as f

Question 15

A programmer needs to replace every occurrence of 'cat' with 'dog' in a string s, but only if 'cat' is not preceded by 'big'. Which regex substitution would achieve this?

Accepted Answer

re.sub(r'(?<!big)cat', 'dog', s). Uses a negative lookbehind assertion `(?<!big)` to match 'cat' only when it is NOT preceded by 'big'. This ensures that 'bigcat' remains unchanged while standalone 'cat' is replaced with 'dog'. The `re.sub` function then substitutes all such matches in the string.

Answer

re.sub(r'bigcat', 'dog', s)

Answer

re.sub(r'cat', 'dog', s)

Answer

re.sub(r'(?<=big)cat', 'dog', s)