PCAP Practice Test 30 — 15 Questions

Question 1

A Python package 'analytics' contains a subpackage 'models' with module 'regression.py'. Inside 'regression.py', there is a function 'linear_fit' that depends on 'numpy'. The developer wants to ensure that 'numpy' is imported only once and available throughout the package. Where should the import 'import numpy as np' be placed?

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

Accepted Answer

In each module that uses numpy, add 'import numpy as np'.. To use numpy in regression.py, that module must have its own import statement, e.g., 'import numpy as np'. Python caches modules in sys.modules, so loading happens only once regardless of where the import statement appears. Thus, repeating 'import numpy as np' in each module that needs it is both correct and efficient, and it respects namespace isolation.

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In the '__init__.py' of the 'models' subpackage.

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In the '__init__.py' of the 'analytics' top-level package.

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In a separate file 'common_imports.py' and import that file everywhere.

Question 2

An abstract base class (ABC) defines an abstract method `process()`. Several subclasses implement it. A function accepts any subclass and calls `process()`. This demonstrates which OOP concept?

Accepted Answer

Polymorphism.. Polymorphism allows objects of different subclasses to be treated uniformly through their common interface. When a function accepts any subclass of the ABC and calls `process()`, the correct implementation is resolved at runtime via dynamic dispatch, which is the essence of polymorphism in Python.

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Inheritance.

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Encapsulation.

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Method overloading.

Question 3

Which of the following is true regarding Python's method resolution order (MRO) in multiple inheritance?

Accepted Answer

The MRO is computed using the C3 linearization algorithm, ensuring that each class appears before its parents and that monotonicity is preserved.. Python's method resolution order (MRO) is computed using the C3 linearization algorithm. This algorithm ensures that each class appears before its parents and that monotonicity is preserved, meaning the order of class precedence does not change when new subclasses are introduced. This is essential for resolving method calls in multiple inheritance scenarios, particularly with diamond inheritance.

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The MRO is always the same as the order of base classes specified in the class statement.

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The MRO can be changed at runtime by modifying the __bases__ attribute of a class.

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The MRO is determined by the order of base classes in the class definition, using a depth-first, left-to-right search without consideration of diamond inheritance.

Question 4

A company is developing a scientific simulation framework where many different solvers must be interchangeable. The framework should enforce that each solver implements methods 'initialize' and 'step'. Developers want to use abstract base classes. Which approach should the team take to ensure that any subclass of 'Solver' cannot be instantiated unless it defines both methods?

Accepted Answer

Inherit from ABC and decorate both methods with @abstractmethod. Inheriting from `ABC` (from the `abc` module) and decorating both `initialize` and `step` with `@abstractmethod` enforces that any concrete subclass must override these methods. Attempting to instantiate a subclass that does not implement all abstract methods raises a `TypeError`, ensuring compile-time-like safety at runtime.

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Define an interface in a separate module and check using isinstance

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Use @abstractmethod without inheriting from ABC

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Define Solver with methods that raise NotImplementedError

Question 5

A company needs to model different types of employees. They have a base class `Employee` with a method `calculate_pay()`. For hourly employees, pay = hours * rate; for salaried employees, pay = salary. Which design approach is most appropriate?

Accepted Answer

Create subclasses `HourlyEmployee` and `SalariedEmployee` that override `calculate_pay()`.. It applies polymorphism through method overriding: each subclass (`HourlyEmployee`, `SalariedEmployee`) provides its own implementation of `calculate_pay()`, allowing the calling code to treat all employees uniformly via the base class interface. This adheres to the Open/Closed Principle and keeps the design extensible without modifying existing code when new employee types are added.

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Use a `@staticmethod` inside `Employee` to compute pay based on a type parameter.

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Define a module-level function that takes an employee object and computes pay.

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Use a single `Employee` class with conditional statements to differentiate pay types.

Question 6

Given the following code: class Parent: def show(self): print('Parent') class Child(Parent): def show(self): print('Child') c = Child(); c.show(); super(Child, c).show(). What is the output?

Accepted Answer

Child Parent. The code first calls `c.show()`, which invokes the overridden `show()` method in the `Child` class, printing 'Child'. Then `super(Child, c).show()` calls the `show()` method of the `Parent` class (the superclass of `Child`) on the same instance `c`, printing 'Parent'. Thus the output is 'Child Parent'.

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Parent Child

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Child Child

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Parent Parent

Question 7

A user entered a string '   Hello, World!   '. Which expression returns 'Hello, World!'?

Accepted Answer

s.strip(). The `strip()` method removes all leading and trailing whitespace characters from a string, returning a new string without the surrounding spaces. In this case, `s.strip()` removes the three leading spaces and three trailing spaces from '   Hello, World!   ', resulting in 'Hello, World!'.

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s.split()

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s.rstrip()

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s.lstrip()

Question 8

What is the result of the expression 'Hello'[1:3]?

Accepted Answer

'el'. In Python, string slicing uses the syntax `string[start:stop]`, where `start` is inclusive and `stop` is exclusive. For `'Hello'[1:3]`, the indices are: index 1 = 'e', index 2 = 'l', and index 3 is not included, so the slice returns 'el'. This is a fundamental string slicing behavior defined in Python's sequence protocol.

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'lo'

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'He'

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'ell'

Question 9

Which THREE of the following escape sequences are valid in a Python string and represent a single character? (Select exactly three.)

Accepted Answer

\'. The backslash followed by a single quote (\') is a valid escape sequence in Python that represents a literal single quote character, allowing it to appear inside a single-quoted string without terminating the string. This sequence is interpreted as a single character by the Python parser.

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\x

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\q

Question 10

A team uses virtual environments to manage dependencies. They need to ensure that a script runs with the exact same module versions across different environments. Which approach is best?

Accepted Answer

Run pip freeze and store the output in a requirements.txt file, then use pip install -r on other systems.. `pip freeze` outputs the exact versions of all installed packages in the current environment, and storing that output in a `requirements.txt` file allows you to reproduce the same environment on another system by running `pip install -r requirements.txt`. This ensures deterministic dependency management across different environments, which is the standard practice for reproducible builds in Python.

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Use sys.path.append to add module directories.

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Copy the entire virtual environment folder to other systems.

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Include the modules in a __pycache__ directory.

Question 11

Which THREE of the following statements about Python packages and modules are true?

Accepted Answer

A module is a single .py file containing Python definitions and statements.. A module in Python is defined as a single .py file that contains Python definitions, such as functions, classes, and variables, as well executable statements. This is the fundamental unit of code organization in Python, and any .py file can be imported as a module.

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The sys.path list is read-only and cannot be modified at runtime.

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A package must contain an __init__.py file to be importable.

Question 12

A developer needs to extract the file extension from a filename like 'document.pdf'. Which expression returns 'pdf'?

Accepted Answer

filename.rsplit('.', 1)[-1]. `rsplit('.', 1)[-1]` splits the string from the right at the last occurrence of the dot, limiting to one split, and then retrieves the last element (index -1), which is the file extension. This handles filenames with multiple dots (e.g., 'archive.tar.gz') correctly, returning only the final extension.

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filename.split('.')[1]

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filename.split('.')[0]

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filename[-3:]

Question 13

Consider the code fragment: 
    f = open('data.txt', 'r')
    data = f.read()
    process_data(data)
    f.close()
What is the primary risk if an exception occurs during process_data(data)?

Accepted Answer

The file descriptor may be leaked because the close() call is skipped.. If `process_data(data)` raises an exception, the `f.close()` statement is never executed, leaving the file descriptor open. This is a resource leak that can exhaust system file handles, especially in long-running applications. Python's `with` statement is the recommended approach to guarantee automatic cleanup even when exceptions occur.

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The exception will be silently suppressed.

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The file will be automatically closed by Python's garbage collector immediately.

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The file contents will be corrupted.

Question 14

A class `Circle` has a class attribute `pi = 3.14`. An instance `c = Circle()` sets `c.pi = 3.14159`. What is the value of `Circle.pi` after this assignment?

Accepted Answer

3.14. In Python, attribute assignment on an instance always creates or modifies an instance attribute, even if a class attribute with the same name exists. The class attribute is only modified when assigned via the class itself, such as `Circle.pi = value`. Here, `c.pi = 3.14159` adds an instance attribute to `c`, leaving `Circle.pi` at 3.14.

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An AttributeError is raised because class attributes cannot be shadowed.

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The value is undefined because class attributes are immutable.

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3.14159

Question 15

Refer to the exhibit. What happens when the code is executed?

Accepted Answer

A TypeError is raised. The code attempts to modify a string by assigning a new character to an index position (s[0] = 'H'). Strings in Python are immutable, meaning their elements cannot be changed after creation. This operation raises a TypeError because the item assignment is not supported for string objects.

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The string becomes "Hallo"

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A SyntaxError is raised

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The code runs without error and s remains "Hello"