PCPP1 Advanced Object Oriented Programming — All Questions With Answers

Question 1hardmultiple choice

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In the context of the Descriptor Protocol, what is the primary difference between a data descriptor and a non-data descriptor?

Question 2mediummultiple choice

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You are implementing a Singleton pattern using the new method. Why is it considered best practice to also define a call method in the metaclass or use a decorator instead of just overriding new in the base class?

Question 3hardmultiple choice

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Consider a class that uses a metaclass to automatically register subclasses in a dictionary. If you want to prevent the base class itself from being registered, how should the metaclass be implemented?

Question 4hardmultiple choice

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What happens if you use a decorator on a class that returns a modified version of the class?

Question 5hardmulti select

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Which THREE of the following statements are correct about Python metaclasses?

Question 6hardmulti select

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Which THREE of the following are true about the Python descriptor protocol?

Question 7easymultiple choice

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You are reviewing a class `BankAccount` that uses a private attribute `balance`. A colleague writes a subclass `SavingsAccount` and tries to access `self.balance` directly, but receives an `AttributeError`. Which statement best explains why this occurs and how to correctly access the balance from the subclass?

Question 8mediummultiple choice

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You are implementing a class `Vector` that supports addition of two vectors. You want `v1 + v2` to return a new `Vector`, and you also want `v1 + 5` to be valid by treating 5 as a scalar and adding it to each component. A colleague suggests implementing `add` to handle both cases. Which implementation strategy is most appropriate?

Question 9hardmulti select

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You are implementing a custom descriptor to validate that an attribute is always a positive number. The descriptor is assigned to a class attribute. Which TWO of the following statements are correct about how descriptors work in this scenario? (Choose two.)

Question 10mediummulti select

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You are designing a plugin system where each plugin is a subclass of `PluginBase`. You want to automatically register each plugin subclass at the time the subclass is defined, without requiring explicit registration calls. You decide to use `__init_subclass`. Which two statements are correct about using `init_subclass__` for this purpose? (Choose two.)

Question 11easymultiple choice

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You are reviewing a class that uses multiple inheritance. The class `Child` inherits from `Base1` and `Base2`, both of which define a method `greet()`. You want `Child.greet()` to call both parent implementations in the order they appear in the MRO. Which code correctly achieves this?

Question 12hardmulti select

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A developer is comparing `__init_subclass` and metaclasses for customizing subclass creation. They want to choose the lighter-weight mechanism when possible. Which two statements correctly describe advantages of `init_subclass__` over defining a custom metaclass in this context? (Choose two.)

Question 13hardmultiple choice

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You are creating a class `Config` that should allow attribute access via both dot notation and dictionary-style keys, e.g., `config.host` and `config['host']`. You also want to prevent adding new attributes after initialization. Which combination of magic methods should you implement?

Question 14mediummulti select

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A framework defines an abstract base class `Shape` using `abc.ABC` with an abstract method `area`. A developer writes a subclass `Circle` that implements `area` but also wants to prevent `Circle` itself from being instantiated directly, requiring users to subclass `Circle` further. Which two techniques achieve that goal while preserving the abstract contract? (Choose two.)

Question 15hardmultiple choice

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You are implementing a class `Logger` that should ensure only one instance exists throughout the application. You decide to use the `new` method to control instantiation. Which implementation correctly enforces the singleton pattern while allowing subclassing?

Question 16mediummultiple choice

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How do you correctly call a method from a sibling class in a diamond inheritance structure using super()?

Question 17easymultiple choice

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Which magic method is responsible for providing the informal string representation of an object, typically used for user-facing output?

Question 18hardmultiple choice

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What is the result of applying the @staticmethod decorator to a method inside a class that also defines a metaclass?

Question 19mediummultiple choice

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You are implementing the Observer pattern. Why should you avoid using a strong reference to the observers in the subject's list?

Question 20mediummultiple choice

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When using abstract base classes (ABCs) from the abc module, what happens if a class inherits from an ABC but fails to implement one of the abstract methods?

Question 21easymultiple choice

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Which magic method should you implement to make your objects support the 'with' statement context manager?

Question 22easymultiple choice

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Which of the following describes the purpose of the slots attribute in a class?

Question 23mediummultiple choice

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In the context of the Factory pattern in Python, what is a typical benefit of using a registry-based approach instead of a large if-else block?

Question 24mediummultiple choice

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When overriding the getattr method, what must you be careful to avoid?

Question 25mediummultiple choice

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Which magic method allows an object to behave like a function?

Question 26hardmultiple choice

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What is the effect of setting slots in a parent class on a child class that does not define its own slots?

Question 27hardmultiple choice

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If you define a class with a metaclass that has a custom call method, when is that call method executed?

Question 28mediummultiple choice

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When implementing the Singleton pattern, what is the advantage of using a module-level instance over a class-based Singleton?

Question 29easymultiple choice

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Which magic method is used to control how an instance is displayed when using the print() function?

Question 30hardmultiple choice

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Why might you use the __init_subclass__ hook instead of a metaclass?

Question 31mediummultiple choice

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When designing a class hierarchy, what is the best way to prevent a method from being overridden by subclasses?

Question 32mediummultiple choice

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In the context of the Observer pattern, what is the benefit of an event-driven system over a direct-method-call approach?

Question 33easymultiple choice

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What is the primary difference between @classmethod and @staticmethod?

Question 34hardmultiple choice

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Why does the 'abc' module provide the 'ABCMeta' metaclass?

Question 35mediummultiple choice

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In the Factory pattern, what should you do if the requested type is unknown?

Question 36hardmultiple choice

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What is the purpose of the 'weakref' module in relation to the Observer pattern?

Question 37easymultiple choice

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Which method is used to customize the behavior of the 'in' operator?

Question 38hardmultiple choice

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How do you define a property in a class to make it read-only?

Question 39mediummultiple choice

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What does the @abstractmethod decorator do when applied to a method inside an ABC?

Question 40mediummultiple choice

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What is the consequence of not calling super().init() in a class with multiple inheritance?

Question 41easymultiple choice

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Which magic method enables index access (e.g., obj[i])?

Question 42mediummultiple choice

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How do you implement the 'Strategy' pattern in Python?

Question 43mediummultiple choice

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What is the difference between a class-level variable and an instance-level variable?

Question 44mediummultiple choice

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What is the purpose of the 'type' function when called with three arguments?

Question 45easymultiple choice

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Which magic method is triggered when an object is deleted using the 'del' keyword?

Question 46mediummulti select

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Which TWO of the following are valid ways to create a singleton in Python?

Question 47mediummulti select

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Which TWO of the following are true regarding multiple inheritance in Python?

Question 48mediummulti select

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Which TWO of the following are correct regarding the 'with' statement in Python?

Question 49mediummulti select

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Which TWO of the following are true about magic methods?

Question 50easymultiple choice

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What is the purpose of the repr method?

Question 51mediummultiple choice

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When using the call method to implement a decorator, what does the decorator receive as an argument?

Question 52hardmulti select

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Which THREE of the following are potential pitfalls of the Singleton pattern in Python?

Question 53mediummultiple choice

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In the context of the Factory pattern, what does a concrete factory implement?

Question 54hardmultiple choice

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What is the primary risk of using 'getattr' without a default value?

Question 55easymultiple choice

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Which function is used to check if an object is an instance of a class?

Question 56hardmulti select

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Which THREE of the following represent common issues when using slots?

Question 57mediummultiple choice

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Why should you use super() instead of calling the parent class method directly by name?

Question 58easymultiple choice

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What happens when you add two objects of a class that implements add?

Question 59hardmultiple choice

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Why does the init method not return anything?

Question 60hardmultiple choice

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What is the purpose of the __set_name__ method in descriptors?

Question 61mediummultiple choice

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When using a metaclass, how can you access the class attributes during the class definition?

Question 62mediummultiple choice

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You are designing a plugin system where each plugin class must automatically register itself with a central registry when defined, without requiring an explicit decorator or registration call. You decide to use the __init_subclass__ hook in the base Plugin class. Which statement correctly describes how to implement this so that every subclass is registered with its own class object?

Question 63mediummultiple choice

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You are designing a class `Matrix` that supports element-wise addition and scalar multiplication. You want `m1 + m2` to return a new `Matrix` without modifying `m1` or `m2`. You have implemented `add` correctly. A colleague writes `m1 += m2` and expects `m1` to be rebound to a new `Matrix` object. However, after the statement, `m1` still refers to the same object and its internal data has been modified in place. Which change to your class is the most likely cause of this behavior?

Question 64hardmultiple choice

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You are implementing a class that represents a monetary amount. You want the expression amount1 + amount2 to return a new Money instance, and you also want amount1 + 5 to work by treating 5 as a Money with zero cents. However, 5 + amount1 should raise a TypeError. Which implementation achieves this behavior?

Question 65mediummultiple choice

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A developer creates a class named `Registry` in a module. The class inherits from `ABCMeta` and defines a `new` method that performs validation on the class namespace before the class is created. Inside `new`, the developer needs to inspect the attributes defined in the class body of the class being created. Which parameter of `new` provides direct access to those attributes?

Question 66mediummultiple choice

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You are designing a class `Connection` that must ensure only one instance exists and that the same instance is returned whenever `Connection()` is called. You implement this using `new` to control instance creation, and you also define `init`. During testing, you notice that `init` runs every time `Connection()` is called, even though `new` returns the existing singleton instance. What is the most appropriate way to prevent `init` from reinitializing the singleton on subsequent calls?

Question 67easymultiple choice

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You are creating a class where you want to prevent instances from having a dict to save memory. You add slots = ('x', 'y') to the class. Which statement is true about this class?

Question 68mediummultiple choice

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You are designing a class hierarchy for a document processing system. The base class `Document` defines a method `render()` that returns a string. You want subclasses to be forced to provide their own implementation, and you want to prevent `Document` from being instantiated directly. Which code correctly enforces this requirement?

Question 69mediummultiple choice

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A developer defines a class `Temperature` that stores a Celsius value in `self._celsius` and exposes a `celsius` property with a setter that validates the value is not below absolute zero. After instantiating `t = Temperature(20)`, the developer runs `t.celsius = -300`. What happens?

Question 70hardmultiple choice

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You are implementing a class `Vector` that supports addition and scalar multiplication. You want `v1 + v2` to return a new `Vector`, and `v1 * 3` to return a new scaled `Vector`. You also want `3 * v1` to work identically. Which pair of methods must you implement to support both `v1 * 3` and `3 * v1` correctly, assuming `v1` is a `Vector` and `3` is an `int`?

Question 71easymultiple choice

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A developer wants to ensure that a method `area` in a base class `Shape` must be overridden by any concrete subclass. The developer writes `class Shape(ABC):` and `@abstractmethod def area(self): ...`. A colleague then creates `class Circle(Shape):` without implementing `area` and tries to instantiate `Circle()`. What happens?

Question 72hardmultiple choice

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A library defines a base class `Plugin` with `__init_subclass(cls, **kwargs)` that automatically registers every subclass in a global registry using `cls.name__`. A developer writes `class MyPlugin(Plugin, priority=5): pass` but the registration fails with a TypeError about unexpected keyword arguments. What is the most likely cause?

Question 73hardmultiple choice

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A developer defines `class Config:` with `slots = ('host', 'port')`. Later, they want to add a new attribute `timeout` to an existing instance without modifying the class. They write `cfg.timeout = 30` and receive an `AttributeError`. Which change would allow per-instance `timeout` assignment while keeping `slots` for `host` and `port`?

Question 74mediummultiple choice

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A developer writes a class `Money` that implements `eq` to compare amounts and currencies, but does not implement `hash`. Instances of `Money` are then used as keys in a `set`. What is the result?

Question 75mediummultiple choice

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You are designing a plugin registry that must automatically register every concrete subclass of a base class `Plugin` at the moment the subclass is defined, without requiring any explicit registration call in the subclass body. You want to avoid a metaclass because the project already uses `ABCMeta` for the base class and you do not want to introduce metaclass conflicts. Which approach best satisfies this requirement?

Question 76mediummultiple choice

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A developer is implementing the Observer pattern and wants to store a list of observers without preventing them from being garbage collected when no other references exist. They decide to use `weakref.WeakSet` to hold the observers. Which statement accurately describes the behavior they should expect?

Question 77hardmultiple choice

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A developer implements a class `Vector` with `add` returning a new `Vector`, and also defines `iadd` that mutates `self` in place and returns `self`. A colleague writes `a = Vector(1,2); b = Vector(3,4); c = a; a += b`. What is the state of `c`?

Question 78hardmultiple choice

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You are implementing a class `Matrix` that supports the `+` operator for matrix addition. You want `m1 + m2` to return a new `Matrix`, and you also want `sum([m1, m2, m3])` to work correctly. You define `add` to return a new `Matrix`. However, `sum([m1, m2, m3])` raises a `TypeError`. What is the most likely reason?

Question 79hardmultiple choice

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A teammate writes a `Money` value object that defines `eq` to compare amounts and currencies, and `hash` to hash the same two fields. During a code review you notice that a subclass `Discount` adds a `percentage` field, overrides only `eq` to include that field, and leaves `hash` inherited. Objects of `Discount` are then used as dictionary keys. What is the actual runtime consequence?

Question 80mediummulti select

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A developer is designing a `Shape` base class and wants subclasses to be forced to implement an `area()` method. Which two approaches are valid in Python for enforcing that subclasses provide `area()`? (Choose two.)

Question 81hardmultiple choice

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You are implementing a `Vector` class whose instances should support `v1 + v2` and also `v1 + 5`, where the second form broadcasts the scalar across every component. A colleague suggests relying on `radd` to handle the scalar case. Why is that insufficient?

Question 82mediummultiple choice

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You are writing a class `Temperature` that should support addition and comparison. You want `t1 + t2` to return a new `Temperature` object, and `t1 == t2` to compare their values. Which magic methods must you implement to achieve this?

Question 83easymultiple choice

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A `Temperature` class stores a numeric `celsius` attribute. Callers keep assigning `temp.celsius = -500`, which is physically impossible. You want any assignment below absolute zero to raise `ValueError` while keeping normal attribute access unchanged. Which construct should you implement?

Question 1hardmultiple choice

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In the context of the Descriptor Protocol, what is the primary difference between a data descriptor and a non-data descriptor?

Question 2mediummultiple choice

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You are implementing a Singleton pattern using the new method. Why is it considered best practice to also define a call method in the metaclass or use a decorator instead of just overriding new in the base class?

Question 3hardmultiple choice

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Consider a class that uses a metaclass to automatically register subclasses in a dictionary. If you want to prevent the base class itself from being registered, how should the metaclass be implemented?

Question 4hardmultiple choice

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What happens if you use a decorator on a class that returns a modified version of the class?

Question 5hardmulti select

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Which THREE of the following statements are correct about Python metaclasses?

Question 6hardmulti select

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Which THREE of the following are true about the Python descriptor protocol?

Question 7easymultiple choice

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You are reviewing a class `BankAccount` that uses a private attribute `balance`. A colleague writes a subclass `SavingsAccount` and tries to access `self.balance` directly, but receives an `AttributeError`. Which statement best explains why this occurs and how to correctly access the balance from the subclass?

Question 8mediummultiple choice

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You are implementing a class `Vector` that supports addition of two vectors. You want `v1 + v2` to return a new `Vector`, and you also want `v1 + 5` to be valid by treating 5 as a scalar and adding it to each component. A colleague suggests implementing `add` to handle both cases. Which implementation strategy is most appropriate?

Question 9hardmulti select

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You are implementing a custom descriptor to validate that an attribute is always a positive number. The descriptor is assigned to a class attribute. Which TWO of the following statements are correct about how descriptors work in this scenario? (Choose two.)

Question 10mediummulti select

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You are designing a plugin system where each plugin is a subclass of `PluginBase`. You want to automatically register each plugin subclass at the time the subclass is defined, without requiring explicit registration calls. You decide to use `__init_subclass`. Which two statements are correct about using `init_subclass__` for this purpose? (Choose two.)

Question 11easymultiple choice

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You are reviewing a class that uses multiple inheritance. The class `Child` inherits from `Base1` and `Base2`, both of which define a method `greet()`. You want `Child.greet()` to call both parent implementations in the order they appear in the MRO. Which code correctly achieves this?

Question 12hardmulti select

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A developer is comparing `__init_subclass` and metaclasses for customizing subclass creation. They want to choose the lighter-weight mechanism when possible. Which two statements correctly describe advantages of `init_subclass__` over defining a custom metaclass in this context? (Choose two.)

Question 13hardmultiple choice

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You are creating a class `Config` that should allow attribute access via both dot notation and dictionary-style keys, e.g., `config.host` and `config['host']`. You also want to prevent adding new attributes after initialization. Which combination of magic methods should you implement?

Question 14mediummulti select

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A framework defines an abstract base class `Shape` using `abc.ABC` with an abstract method `area`. A developer writes a subclass `Circle` that implements `area` but also wants to prevent `Circle` itself from being instantiated directly, requiring users to subclass `Circle` further. Which two techniques achieve that goal while preserving the abstract contract? (Choose two.)

Question 15hardmultiple choice

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You are implementing a class `Logger` that should ensure only one instance exists throughout the application. You decide to use the `new` method to control instantiation. Which implementation correctly enforces the singleton pattern while allowing subclassing?

Question 16mediummultiple choice

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How do you correctly call a method from a sibling class in a diamond inheritance structure using super()?

Question 17easymultiple choice

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Which magic method is responsible for providing the informal string representation of an object, typically used for user-facing output?

Question 18hardmultiple choice

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What is the result of applying the @staticmethod decorator to a method inside a class that also defines a metaclass?

Question 19mediummultiple choice

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You are implementing the Observer pattern. Why should you avoid using a strong reference to the observers in the subject's list?

Question 20mediummultiple choice

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When using abstract base classes (ABCs) from the abc module, what happens if a class inherits from an ABC but fails to implement one of the abstract methods?

Question 21easymultiple choice

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Which magic method should you implement to make your objects support the 'with' statement context manager?

Question 22easymultiple choice

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Which of the following describes the purpose of the slots attribute in a class?

Question 23mediummultiple choice

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In the context of the Factory pattern in Python, what is a typical benefit of using a registry-based approach instead of a large if-else block?

Question 24mediummultiple choice

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When overriding the getattr method, what must you be careful to avoid?

Question 25mediummultiple choice

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Which magic method allows an object to behave like a function?

Question 26hardmultiple choice

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What is the effect of setting slots in a parent class on a child class that does not define its own slots?

Question 27hardmultiple choice

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If you define a class with a metaclass that has a custom call method, when is that call method executed?

Question 28mediummultiple choice

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When implementing the Singleton pattern, what is the advantage of using a module-level instance over a class-based Singleton?

Question 29easymultiple choice

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Which magic method is used to control how an instance is displayed when using the print() function?

Question 30hardmultiple choice

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Why might you use the __init_subclass__ hook instead of a metaclass?

Question 31mediummultiple choice

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When designing a class hierarchy, what is the best way to prevent a method from being overridden by subclasses?

Question 32mediummultiple choice

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In the context of the Observer pattern, what is the benefit of an event-driven system over a direct-method-call approach?

Question 33easymultiple choice

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What is the primary difference between @classmethod and @staticmethod?

Question 34hardmultiple choice

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Why does the 'abc' module provide the 'ABCMeta' metaclass?

Question 35mediummultiple choice

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In the Factory pattern, what should you do if the requested type is unknown?

Question 36hardmultiple choice

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What is the purpose of the 'weakref' module in relation to the Observer pattern?

Question 37easymultiple choice

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Which method is used to customize the behavior of the 'in' operator?

Question 38hardmultiple choice

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How do you define a property in a class to make it read-only?

Question 39mediummultiple choice

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What does the @abstractmethod decorator do when applied to a method inside an ABC?

Question 40mediummultiple choice

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What is the consequence of not calling super().init() in a class with multiple inheritance?

Question 41easymultiple choice

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Which magic method enables index access (e.g., obj[i])?

Question 42mediummultiple choice

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How do you implement the 'Strategy' pattern in Python?

Question 43mediummultiple choice

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What is the difference between a class-level variable and an instance-level variable?

Question 44mediummultiple choice

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What is the purpose of the 'type' function when called with three arguments?

Question 45easymultiple choice

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Which magic method is triggered when an object is deleted using the 'del' keyword?

Question 46mediummulti select

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Which TWO of the following are valid ways to create a singleton in Python?

Question 47mediummulti select

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Which TWO of the following are true regarding multiple inheritance in Python?

Question 48mediummulti select

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Which TWO of the following are correct regarding the 'with' statement in Python?

Question 49mediummulti select

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Which TWO of the following are true about magic methods?

Question 50easymultiple choice

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What is the purpose of the repr method?

Question 51mediummultiple choice

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When using the call method to implement a decorator, what does the decorator receive as an argument?

Question 52hardmulti select

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Which THREE of the following are potential pitfalls of the Singleton pattern in Python?

Question 53mediummultiple choice

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In the context of the Factory pattern, what does a concrete factory implement?

Question 54hardmultiple choice

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What is the primary risk of using 'getattr' without a default value?

Question 55easymultiple choice

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Which function is used to check if an object is an instance of a class?

Question 56hardmulti select

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Which THREE of the following represent common issues when using slots?

Question 57mediummultiple choice

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Why should you use super() instead of calling the parent class method directly by name?

Question 58easymultiple choice

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What happens when you add two objects of a class that implements add?

Question 59hardmultiple choice

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Why does the init method not return anything?

Question 60hardmultiple choice

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What is the purpose of the __set_name__ method in descriptors?

Question 61mediummultiple choice

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When using a metaclass, how can you access the class attributes during the class definition?

Question 62mediummultiple choice

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You are designing a plugin system where each plugin class must automatically register itself with a central registry when defined, without requiring an explicit decorator or registration call. You decide to use the __init_subclass__ hook in the base Plugin class. Which statement correctly describes how to implement this so that every subclass is registered with its own class object?

Question 63mediummultiple choice

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You are designing a class `Matrix` that supports element-wise addition and scalar multiplication. You want `m1 + m2` to return a new `Matrix` without modifying `m1` or `m2`. You have implemented `add` correctly. A colleague writes `m1 += m2` and expects `m1` to be rebound to a new `Matrix` object. However, after the statement, `m1` still refers to the same object and its internal data has been modified in place. Which change to your class is the most likely cause of this behavior?

Question 64hardmultiple choice

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You are implementing a class that represents a monetary amount. You want the expression amount1 + amount2 to return a new Money instance, and you also want amount1 + 5 to work by treating 5 as a Money with zero cents. However, 5 + amount1 should raise a TypeError. Which implementation achieves this behavior?

Question 65mediummultiple choice

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A developer creates a class named `Registry` in a module. The class inherits from `ABCMeta` and defines a `new` method that performs validation on the class namespace before the class is created. Inside `new`, the developer needs to inspect the attributes defined in the class body of the class being created. Which parameter of `new` provides direct access to those attributes?

Question 66mediummultiple choice

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You are designing a class `Connection` that must ensure only one instance exists and that the same instance is returned whenever `Connection()` is called. You implement this using `new` to control instance creation, and you also define `init`. During testing, you notice that `init` runs every time `Connection()` is called, even though `new` returns the existing singleton instance. What is the most appropriate way to prevent `init` from reinitializing the singleton on subsequent calls?

Question 67easymultiple choice

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You are creating a class where you want to prevent instances from having a dict to save memory. You add slots = ('x', 'y') to the class. Which statement is true about this class?

Question 68mediummultiple choice

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You are designing a class hierarchy for a document processing system. The base class `Document` defines a method `render()` that returns a string. You want subclasses to be forced to provide their own implementation, and you want to prevent `Document` from being instantiated directly. Which code correctly enforces this requirement?

Question 69mediummultiple choice

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A developer defines a class `Temperature` that stores a Celsius value in `self._celsius` and exposes a `celsius` property with a setter that validates the value is not below absolute zero. After instantiating `t = Temperature(20)`, the developer runs `t.celsius = -300`. What happens?

Question 70hardmultiple choice

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You are implementing a class `Vector` that supports addition and scalar multiplication. You want `v1 + v2` to return a new `Vector`, and `v1 * 3` to return a new scaled `Vector`. You also want `3 * v1` to work identically. Which pair of methods must you implement to support both `v1 * 3` and `3 * v1` correctly, assuming `v1` is a `Vector` and `3` is an `int`?

Question 71easymultiple choice

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A developer wants to ensure that a method `area` in a base class `Shape` must be overridden by any concrete subclass. The developer writes `class Shape(ABC):` and `@abstractmethod def area(self): ...`. A colleague then creates `class Circle(Shape):` without implementing `area` and tries to instantiate `Circle()`. What happens?

Question 72hardmultiple choice

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A library defines a base class `Plugin` with `__init_subclass(cls, **kwargs)` that automatically registers every subclass in a global registry using `cls.name__`. A developer writes `class MyPlugin(Plugin, priority=5): pass` but the registration fails with a TypeError about unexpected keyword arguments. What is the most likely cause?

Question 73hardmultiple choice

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A developer defines `class Config:` with `slots = ('host', 'port')`. Later, they want to add a new attribute `timeout` to an existing instance without modifying the class. They write `cfg.timeout = 30` and receive an `AttributeError`. Which change would allow per-instance `timeout` assignment while keeping `slots` for `host` and `port`?

Question 74mediummultiple choice

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A developer writes a class `Money` that implements `eq` to compare amounts and currencies, but does not implement `hash`. Instances of `Money` are then used as keys in a `set`. What is the result?

Question 75mediummultiple choice

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You are designing a plugin registry that must automatically register every concrete subclass of a base class `Plugin` at the moment the subclass is defined, without requiring any explicit registration call in the subclass body. You want to avoid a metaclass because the project already uses `ABCMeta` for the base class and you do not want to introduce metaclass conflicts. Which approach best satisfies this requirement?

Question 76mediummultiple choice

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A developer is implementing the Observer pattern and wants to store a list of observers without preventing them from being garbage collected when no other references exist. They decide to use `weakref.WeakSet` to hold the observers. Which statement accurately describes the behavior they should expect?

Question 77hardmultiple choice

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A developer implements a class `Vector` with `add` returning a new `Vector`, and also defines `iadd` that mutates `self` in place and returns `self`. A colleague writes `a = Vector(1,2); b = Vector(3,4); c = a; a += b`. What is the state of `c`?

Question 78hardmultiple choice

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You are implementing a class `Matrix` that supports the `+` operator for matrix addition. You want `m1 + m2` to return a new `Matrix`, and you also want `sum([m1, m2, m3])` to work correctly. You define `add` to return a new `Matrix`. However, `sum([m1, m2, m3])` raises a `TypeError`. What is the most likely reason?

Question 79hardmultiple choice

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A teammate writes a `Money` value object that defines `eq` to compare amounts and currencies, and `hash` to hash the same two fields. During a code review you notice that a subclass `Discount` adds a `percentage` field, overrides only `eq` to include that field, and leaves `hash` inherited. Objects of `Discount` are then used as dictionary keys. What is the actual runtime consequence?

Question 80mediummulti select

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A developer is designing a `Shape` base class and wants subclasses to be forced to implement an `area()` method. Which two approaches are valid in Python for enforcing that subclasses provide `area()`? (Choose two.)

Question 81hardmultiple choice

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You are implementing a `Vector` class whose instances should support `v1 + v2` and also `v1 + 5`, where the second form broadcasts the scalar across every component. A colleague suggests relying on `radd` to handle the scalar case. Why is that insufficient?

Question 82mediummultiple choice

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You are writing a class `Temperature` that should support addition and comparison. You want `t1 + t2` to return a new `Temperature` object, and `t1 == t2` to compare their values. Which magic methods must you implement to achieve this?

Question 83easymultiple choice

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A `Temperature` class stores a numeric `celsius` attribute. Callers keep assigning `temp.celsius = -500`, which is physically impossible. You want any assignment below absolute zero to raise `ValueError` while keeping normal attribute access unchanged. Which construct should you implement?

PCPP1 Advanced Object Oriented Programming — All Questions With Answers

In the context of the Descriptor Protocol, what is the primary difference between a data descriptor and a non-data descriptor?

You are implementing a Singleton pattern using the __new__ method. Why is it considered best practice to also define a __call__ method in the metaclass or use a decorator instead of just overriding __new__ in the base class?

Consider a class that uses a metaclass to automatically register subclasses in a dictionary. If you want to prevent the base class itself from being registered, how should the metaclass be implemented?

What happens if you use a decorator on a class that returns a modified version of the class?

Which THREE of the following statements are correct about Python metaclasses?

Which THREE of the following are true about the Python descriptor protocol?

You are implementing a custom descriptor to validate that an attribute is always a positive number. The descriptor is assigned to a class attribute. Which TWO of the following statements are correct about how descriptors work in this scenario? (Choose two.)

You are reviewing a class that uses multiple inheritance. The class `Child` inherits from `Base1` and `Base2`, both of which define a method `greet()`. You want `Child.greet()` to call both parent implementations in the order they appear in the MRO. Which code correctly achieves this?

A developer is comparing `__init_subclass__` and metaclasses for customizing subclass creation. They want to choose the lighter-weight mechanism when possible. Which two statements correctly describe advantages of `__init_subclass__` over defining a custom metaclass in this context? (Choose two.)

You are creating a class `Config` that should allow attribute access via both dot notation and dictionary-style keys, e.g., `config.host` and `config['host']`. You also want to prevent adding new attributes after initialization. Which combination of magic methods should you implement?

You are implementing a class `Logger` that should ensure only one instance exists throughout the application. You decide to use the `__new__` method to control instantiation. Which implementation correctly enforces the singleton pattern while allowing subclassing?

How do you correctly call a method from a sibling class in a diamond inheritance structure using super()?

Which magic method is responsible for providing the informal string representation of an object, typically used for user-facing output?

What is the result of applying the @staticmethod decorator to a method inside a class that also defines a metaclass?

You are implementing the Observer pattern. Why should you avoid using a strong reference to the observers in the subject's list?

When using abstract base classes (ABCs) from the abc module, what happens if a class inherits from an ABC but fails to implement one of the abstract methods?

Which magic method should you implement to make your objects support the 'with' statement context manager?

Which of the following describes the purpose of the __slots__ attribute in a class?

In the context of the Factory pattern in Python, what is a typical benefit of using a registry-based approach instead of a large if-else block?

When overriding the __getattr__ method, what must you be careful to avoid?

Which magic method allows an object to behave like a function?

What is the effect of setting __slots__ in a parent class on a child class that does not define its own __slots__?

If you define a class with a metaclass that has a custom __call__ method, when is that __call__ method executed?

When implementing the Singleton pattern, what is the advantage of using a module-level instance over a class-based Singleton?

Which magic method is used to control how an instance is displayed when using the print() function?

Why might you use the __init_subclass__ hook instead of a metaclass?

When designing a class hierarchy, what is the best way to prevent a method from being overridden by subclasses?

In the context of the Observer pattern, what is the benefit of an event-driven system over a direct-method-call approach?

What is the primary difference between @classmethod and @staticmethod?

Why does the 'abc' module provide the 'ABCMeta' metaclass?

In the Factory pattern, what should you do if the requested type is unknown?

What is the purpose of the 'weakref' module in relation to the Observer pattern?

Which method is used to customize the behavior of the 'in' operator?

How do you define a property in a class to make it read-only?

What does the @abstractmethod decorator do when applied to a method inside an ABC?

What is the consequence of not calling super().__init__() in a class with multiple inheritance?

Which magic method enables index access (e.g., obj[i])?

How do you implement the 'Strategy' pattern in Python?

What is the difference between a class-level variable and an instance-level variable?

What is the purpose of the 'type' function when called with three arguments?

Which magic method is triggered when an object is deleted using the 'del' keyword?

Which TWO of the following are valid ways to create a singleton in Python?

Which TWO of the following are true regarding multiple inheritance in Python?

Which TWO of the following are correct regarding the 'with' statement in Python?

Which TWO of the following are true about magic methods?

What is the purpose of the __repr__ method?

When using the __call__ method to implement a decorator, what does the decorator receive as an argument?

Which THREE of the following are potential pitfalls of the Singleton pattern in Python?

In the context of the Factory pattern, what does a concrete factory implement?

What is the primary risk of using 'getattr' without a default value?

Which function is used to check if an object is an instance of a class?

Which THREE of the following represent common issues when using __slots__?

Why should you use super() instead of calling the parent class method directly by name?

What happens when you add two objects of a class that implements __add__?

Why does the __init__ method not return anything?

What is the purpose of the __set_name__ method in descriptors?

When using a metaclass, how can you access the class attributes during the class definition?

You are creating a class where you want to prevent instances from having a __dict__ to save memory. You add __slots__ = ('x', 'y') to the class. Which statement is true about this class?

A developer defines a class `Temperature` that stores a Celsius value in `self._celsius` and exposes a `celsius` property with a setter that validates the value is not below absolute zero. After instantiating `t = Temperature(20)`, the developer runs `t.celsius = -300`. What happens?

A developer writes a class `Money` that implements `__eq__` to compare amounts and currencies, but does not implement `__hash__`. Instances of `Money` are then used as keys in a `set`. What is the result?

A developer implements a class `Vector` with `__add__` returning a new `Vector`, and also defines `__iadd__` that mutates `self` in place and returns `self`. A colleague writes `a = Vector(1,2); b = Vector(3,4); c = a; a += b`. What is the state of `c`?

A developer is designing a `Shape` base class and wants subclasses to be forced to implement an `area()` method. Which two approaches are valid in Python for enforcing that subclasses provide `area()`? (Choose two.)

You are implementing a `Vector` class whose instances should support `v1 + v2` and also `v1 + 5`, where the second form broadcasts the scalar across every component. A colleague suggests relying on `__radd__` to handle the scalar case. Why is that insufficient?

You are writing a class `Temperature` that should support addition and comparison. You want `t1 + t2` to return a new `Temperature` object, and `t1 == t2` to compare their values. Which magic methods must you implement to achieve this?

A `Temperature` class stores a numeric `celsius` attribute. Callers keep assigning `temp.celsius = -500`, which is physically impossible. You want any assignment below absolute zero to raise `ValueError` while keeping normal attribute access unchanged. Which construct should you implement?

PCPP1 Advanced Object Oriented Programming — All Questions With Answers

In the context of the Descriptor Protocol, what is the primary difference between a data descriptor and a non-data descriptor?

You are implementing a Singleton pattern using the __new__ method. Why is it considered best practice to also define a __call__ method in the metaclass or use a decorator instead of just overriding __new__ in the base class?

Consider a class that uses a metaclass to automatically register subclasses in a dictionary. If you want to prevent the base class itself from being registered, how should the metaclass be implemented?

What happens if you use a decorator on a class that returns a modified version of the class?

Which THREE of the following statements are correct about Python metaclasses?

Which THREE of the following are true about the Python descriptor protocol?

You are implementing a custom descriptor to validate that an attribute is always a positive number. The descriptor is assigned to a class attribute. Which TWO of the following statements are correct about how descriptors work in this scenario? (Choose two.)

You are reviewing a class that uses multiple inheritance. The class `Child` inherits from `Base1` and `Base2`, both of which define a method `greet()`. You want `Child.greet()` to call both parent implementations in the order they appear in the MRO. Which code correctly achieves this?

A developer is comparing `__init_subclass__` and metaclasses for customizing subclass creation. They want to choose the lighter-weight mechanism when possible. Which two statements correctly describe advantages of `__init_subclass__` over defining a custom metaclass in this context? (Choose two.)

You are creating a class `Config` that should allow attribute access via both dot notation and dictionary-style keys, e.g., `config.host` and `config['host']`. You also want to prevent adding new attributes after initialization. Which combination of magic methods should you implement?

You are implementing a class `Logger` that should ensure only one instance exists throughout the application. You decide to use the `__new__` method to control instantiation. Which implementation correctly enforces the singleton pattern while allowing subclassing?

How do you correctly call a method from a sibling class in a diamond inheritance structure using super()?

Which magic method is responsible for providing the informal string representation of an object, typically used for user-facing output?

You are implementing a Singleton pattern using the new method. Why is it considered best practice to also define a call method in the metaclass or use a decorator instead of just overriding new in the base class?

A developer is comparing `__init_subclass` and metaclasses for customizing subclass creation. They want to choose the lighter-weight mechanism when possible. Which two statements correctly describe advantages of `init_subclass__` over defining a custom metaclass in this context? (Choose two.)

You are implementing a class `Logger` that should ensure only one instance exists throughout the application. You decide to use the `new` method to control instantiation. Which implementation correctly enforces the singleton pattern while allowing subclassing?

Which of the following describes the purpose of the slots attribute in a class?

When overriding the getattr method, what must you be careful to avoid?

What is the effect of setting slots in a parent class on a child class that does not define its own slots?

If you define a class with a metaclass that has a custom call method, when is that call method executed?

What is the consequence of not calling super().init() in a class with multiple inheritance?

What is the purpose of the repr method?

When using the call method to implement a decorator, what does the decorator receive as an argument?

Which THREE of the following represent common issues when using slots?

What happens when you add two objects of a class that implements add?

Why does the init method not return anything?

You are creating a class where you want to prevent instances from having a dict to save memory. You add slots = ('x', 'y') to the class. Which statement is true about this class?

A developer writes a class `Money` that implements `eq` to compare amounts and currencies, but does not implement `hash`. Instances of `Money` are then used as keys in a `set`. What is the result?

A developer implements a class `Vector` with `add` returning a new `Vector`, and also defines `iadd` that mutates `self` in place and returns `self`. A colleague writes `a = Vector(1,2); b = Vector(3,4); c = a; a += b`. What is the state of `c`?

You are implementing a `Vector` class whose instances should support `v1 + v2` and also `v1 + 5`, where the second form broadcasts the scalar across every component. A colleague suggests relying on `radd` to handle the scalar case. Why is that insufficient?

You are implementing a Singleton pattern using the new method. Why is it considered best practice to also define a call method in the metaclass or use a decorator instead of just overriding new in the base class?

A developer is comparing `__init_subclass` and metaclasses for customizing subclass creation. They want to choose the lighter-weight mechanism when possible. Which two statements correctly describe advantages of `init_subclass__` over defining a custom metaclass in this context? (Choose two.)

You are implementing a class `Logger` that should ensure only one instance exists throughout the application. You decide to use the `new` method to control instantiation. Which implementation correctly enforces the singleton pattern while allowing subclassing?

Which of the following describes the purpose of the slots attribute in a class?

When overriding the getattr method, what must you be careful to avoid?

What is the effect of setting slots in a parent class on a child class that does not define its own slots?

If you define a class with a metaclass that has a custom call method, when is that call method executed?

What is the consequence of not calling super().init() in a class with multiple inheritance?

What is the purpose of the repr method?

When using the call method to implement a decorator, what does the decorator receive as an argument?

Which THREE of the following represent common issues when using slots?