Object-Oriented Programming

A developer creates a Python class with a method that is intended to be overridden in subclasses. Which approach best ensures that the method is not accidentally called on the base class?

A developer wants to ensure that a class attribute is shared among all instances but cannot be modified from outside the class. Which approach is most appropriate?

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?

A team is developing a system that must handle different types of documents (PDF, Word, etc.). Each document type has a unique parsing method. To avoid massive conditional logic, which OOP concept should be applied?

A developer writes a class 'Logger' with a class method 'log(msg)' that writes to a file. Another class 'AppLogger' inherits from 'Logger'. The developer expects both classes to share the same file handle. However, after creating an instance of 'AppLogger', the file handle is different. What is the most likely cause?

A class 'MyClass' has a method 'do_something' that uses 'self.__private'. A subclass 'MySubClass' tries to access 'self.__private' and gets an AttributeError. Why?

A Python class 'Shape' defines an abstract method 'area'. Subclasses 'Circle' and 'Square' implement 'area'. A function 'calculate_area(shape)' expects a 'Shape' instance. Which principle ensures that the function works correctly without knowing the specific subclass?

A developer defines a class 'Car' with an attribute 'wheels = 4'. They create two instances: car1 = Car() and car2 = Car(). Then they set car1.wheels = 3. What is the value of car2.wheels?

A class 'Point' is defined with __slots__ = ['x', 'y']. A developer creates an instance p = Point() and tries to set p.z = 10. What happens?

A developer defines a class 'A' with a method 'm' that uses 'self.a'. Class 'B' inherits from 'A' and defines __init__ that sets 'self.a = 10'. An instance of B is created and method m is called. What is the output?

A developer is designing a class hierarchy for a library system. They want to ensure that a method 'borrow' in the base class 'Item' can be overridden by subclasses like 'Book' and 'DVD', but the base implementation should not be callable directly. Which approach best achieves this?

What is the output of the code?

A developer wants to ensure that an attribute 'balance' of a BankAccount class cannot be accessed directly from outside the class but can be accessed through a method. Which approach should be used?

An engineer is debugging an application that uses inheritance. The base class 'Vehicle' defines a method 'start()' that prints 'Vehicle started'. The subclass 'Car' overrides 'start()' to print 'Car started'. The code contains a function that accepts a Vehicle object and calls 'start()'. What is the output if a Car object is passed?

A Python developer is implementing a class that should behave like a sequence and support indexing. Which pair of special methods must be defined to achieve this?

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?

Consider the following code snippet: 'class A: pass; class B(A): pass; class C(A): pass; class D(B, C): pass'. What is the Method Resolution Order (MRO) for class D according to the C3 linearization algorithm used by Python?

Refer to the exhibit. Which THREE statements about the class hierarchy are correct?

Refer to the exhibit. What will happen when the code is executed?

You are working on a legacy system that processes financial transactions. The system uses a class hierarchy: Transaction (base), Deposit, Withdrawal, Transfer. Each subclass overrides a method 'process()' to handle its specific logic. The code often runs in a multi-threaded environment and you notice intermittent errors where a transaction is processed twice. The logging shows that the same transaction object is being passed to the process method multiple times. The transaction objects are created from a factory function that caches recently used transactions. The errors seem to occur when two threads call the factory at the same time with the same parameters. After investigating, you find that the factory uses a class-level dictionary to cache objects. Which of the following is the most appropriate solution to prevent double processing?

Drag and drop the steps to define and call a function with default arguments in Python into the correct order.

Match each Python operator to its precedence level (1=highest).

Match each list method to its effect.

A developer is implementing a simple counter class. The class should start at 0 and increment by 1 each time the 'increment' method is called. Which implementation is correct?

Consider the following class hierarchy: class A: def method(self): return 'A'; class B(A): pass; class C(A): def method(self): return 'C'; class D(B, C): pass. What is the output of D().method() according to Python's MRO?

A developer wants to ensure that the 'radius' attribute of a Circle class is always non-negative. Which implementation using @property is correct?

A class MyClass defines __str__ and __repr__ methods. What is the purpose of __repr__?

Consider the following code: class A: x = 1; class B(A): pass; class C(A): x = 2; class D(B, C): pass. What is D.x?

Which of the following correctly uses an abstract base class to enforce that all subclasses implement a 'make_sound' method? (Assume ABC imported)

A subclass overrides a method but wants to call the parent class's version. Which keyword should be used?

Given: class A: def method(self): print('A'); class B(A): def method(self): super().method(); print('B'); class C(A): def method(self): super().method(); print('C'); class D(B, C): pass. What is printed by D().method()?

Which TWO statements about static methods (@staticmethod) are correct?

Which TWO statements about Python's name mangling are correct?

Refer to the exhibit. Which of the following correctly shows the MRO of class D?

Refer to the exhibit. What is printed?

A developer defines a class with a private attribute `_value` and wants to provide controlled access. Which approach is the most Pythonic?

A parent class defines a method `move()`. A child class overrides `move()` but also needs to call the parent's version inside it. Which syntax allows that?

A developer creates classes `A`, `B(A)`, `C(A)`, and `D(B, C)`. When calling a method from `D` that is defined in `A`, which class's version is used according to Python's MRO?

A class has both `@classmethod` and `@staticmethod` decorators. What is a key difference between them?

A programmer wants to restrict a class to only allow specific attribute names and reduce memory usage. Which feature should they use?

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

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?

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?

Which TWO of the following statements about Python classes are true? (Select exactly 2.)

Which THREE statements about the Python method resolution order (MRO) are true? (Select exactly 3.)

Which TWO of the following are valid ways to define a property in a Python class? (Select exactly 2.)

Refer to the exhibit. What is the output? (Note: actual MRO may vary; choose the one that matches Python 3 C3 linearization.)

A developer wants to ensure that a class attribute is shared across all instances. Which approach should be used?

A programmer writes a class with a method that should be called on the class itself, not on instances. Which decorator is appropriate?

A team is using inheritance but wants to prevent a method from being overridden in subclasses. What Python feature can enforce this?

A class inherits from two parent classes that both have a method with the same name. When calling the method on the child, only one parent's version is executed. What Python mechanism determines which one?

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

A programmer wants to create a class that cannot be instantiated directly, only through a factory method. Which approach should be used?

When a class defines both __getattr__ and __getattribute__, which one is called when accessing an attribute that exists in the instance?

A class defines an __init__ method that takes optional arguments. What is the correct way to provide default values?

Which TWO of the following are valid ways to define a class attribute that is shared among all instances?

Refer to the exhibit. What will be the output when the code is executed?

Refer to the exhibit. What is the root cause of the error?

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?

A team is implementing a shape hierarchy with a base class `Shape` that should have an `area()` method. They want to ensure that every subclass must provide its own implementation of `area()`. Which approach should they use?

A class `ServerConfig` has a class attribute `port = 8080`. After deployment, a developer runs `ServerConfig.port = 9090` in one module, and unexpectedly all existing instances now use port 9090. What concept explains this behavior?

A developer wants to create a class that logs every attribute access on an instance. Which special method should they override?

A class `Point` has an `__init__` that sets `self.x` and `self.y`. They want to compare points by equality (i.e., `p1 == p2` should work correctly). Which method should they implement?

A programmer uses a class method to create an alternative constructor for a `Point` class. The method should parse a string like "10,20" and return a `Point` instance with x=10, y=20. Which code snippet correctly implements this?

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?

A class has a class attribute that is a list. A developer modifies this list via one instance, and the change is reflected in all other instances. What is the best practice to avoid this unintended sharing?

Which of the following correctly uses `__slots__` to restrict attribute creation to only `x` and `y`?

Which TWO of the following are special methods in Python?

Which THREE of the following are true about the `__init__` method in Python?

A developer defines a class with an __init__ method that sets instance attributes. Which of the following is the correct way to call the parent class's __init__ from a child class?

A class named Counter has a class variable count and an instance method increment. The method is defined as def increment(self): Counter.count += 1. What will be the output after executing the following code? c1 = Counter(); c2 = Counter(); c1.increment(); c2.increment(); print(Counter.count, c1.count, c2.count)

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

A programmer wants to ensure that a class attribute is the same for all instances and can be accessed via the class name. Which type of variable should be defined?

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?

A class has a method that does not access any instance or class data. What decorator should be used to define it as a utility method that can be called on the class itself without requiring an instance?

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?

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

Which TWO of the following are valid ways to define a class method in Python? (Select exactly two.)

Which THREE of the following are characteristics of Python's special methods (dunder methods)? (Select exactly three.)

Refer to the exhibit. What happens when the last line is executed?

A developer defines a class hierarchy with multiple inheritance: class A, class B(A), class C(A), class D(B,C). The method 'm' is defined only in A. What is the method resolution order for D according to the C3 linearization algorithm?

A developer wants to implement a read-only property for a class 'Temperature' that returns the temperature in Celsius but prevents external modification. Which code snippet correctly defines such a property?

A developer creates a metaclass 'Meta' that modifies class creation by adding a class attribute 'created_by' set to 'Meta'. Which code snippet correctly defines and uses this metaclass?

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?

A developer wants a class 'LoggedDict' that behaves like a dict but logs all attribute access in the console. Which method override correctly implements this for getting an attribute?

A developer wants a class 'Point' to have a readable string representation that returns 'Point(x, y)'. Which special method should be overridden?

Which THREE of the following are true about Python's object-oriented programming features?

Which TWO statements about method overriding in Python are correct?

A development team is building a real-time chat application using Python. The application uses a class 'ChatRoom' that maintains a list of 'User' objects as active participants. Each User object holds a reference back to its ChatRoom to send messages. Over time, the application runs out of memory. Profiling reveals that User objects are not being garbage collected even after users disconnect. The team suspects circular references. Which solution would effectively resolve the memory leak without breaking the functionality?

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?

A junior developer writes a class 'Logger' that should only ever have one instance (singleton). They attempt to implement it by overriding __new__ to always return the same instance. However, when multiple threads attempt to create a Logger, they sometimes get different instances. Which modification will make the singleton thread-safe?

Which of the following statements about class inheritance in Python are true? (Choose two.)

Which three statements about the Method Resolution Order (MRO) in Python are true? (Choose three.)

A developer is building a simulation of different types of vehicles. They have a base class Vehicle with an attribute speed initialized in __init__. They also have a subclass Car that inherits from Vehicle and adds an attribute fuel_type. The developer wants to ensure that every time a Car object is created, it also initializes the speed attribute from the Vehicle class. Which approach should the developer use?

A junior developer wrote a class representing a bank account with a private attribute balance. They used double underscore prefix (__balance) to make it private. However, in a test script, they are still able to access the attribute using the mangled name _Account__balance. The developer is confused about why encapsulation is not enforced. Which statement best explains this behavior?

A team is developing a data processing pipeline where each step is a class that implements a common interface. They have defined an abstract base class DataProcessor with an abstract method process(data). Several concrete subclasses implement process. Now they need to add a new step that logs the data before processing. They want to reuse the existing processing logic without modifying the original classes. Which design pattern should they apply?

An application uses a class to represent a configuration object that reads settings from a file. The class has a class attribute config_cache that holds a dictionary of loaded configurations to avoid repeated file reads. However, the developer notices that when they modify the dictionary for one instance, it affects all instances. They want to ensure that each instance has its own copy of the configuration data upon initialization. Which change should they make?

A developer is working on a class hierarchy for geometric shapes. They have a base class Shape with an abstract method area(). They also have a mixin class Drawable that provides a method draw(). They want to create a class Rectangle that inherits from both Shape and Drawable. However, they encounter a TypeError when trying to instantiate Rectangle because the abstract method area() is not implemented. Which action should they take to resolve this?

Which TWO of the following statements about class attributes in Python are true?

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

A team is developing a banking system in Python. They have a base class Account with attributes account_number and balance, and a method __init__(self, account_number, balance) that initializes these attributes. They then create a subclass SavingsAccount that adds an attribute interest_rate. In SavingsAccount's __init__, they assign self.interest_rate = rate but do not call super().__init__. When they instantiate SavingsAccount('12345', 1000, 0.02) and attempt to print(balance), an AttributeError occurs: 'SavingsAccount' object has no attribute 'balance'. What is the most appropriate fix to ensure that the SavingsAccount includes balance and account_number without code duplication?

Refer to the exhibit. What is the output of the last line?

Refer to the exhibit. What happens when the last command is executed?

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?

A developer writes a class `Vector` and wants `v1 + v2` to return a brand-new `Vector`, while `v1 += v2` should mutate `v1` in place and return it. Which pair of special methods achieves this behaviour?

A developer writes a class `Logger` with a method `log(self, message)`. They want to ensure that when `Logger` is subclassed, any override of `log` must call the parent's `log` method. Which technique best enforces this requirement in Python?

A team wants a `Logger` class that can be used both as `Logger.log('msg')` on the class itself and as `logger.log('msg')` on an instance, with identical behaviour and no access to instance state. Which decorator should be applied to `log`?

A class `Vector` defines `__add__` to return a new `Vector`. A developer writes `v1 = Vector(1,2); v2 = Vector(3,4); v3 = v1 + v2`. What is the type of `v3`?

A developer writes a class `Circle` with `def __init__(self, radius): self.radius = radius` and wants printing a `Circle` instance to produce a readable description such as `Circle(5)`. Which method should be implemented, and why over the alternative?