Interview Questions
Metaclasses are classes for classes, allowing customization of class creation. Used for API enforcement, attribute validation, class registration, abstract base classes. Created using type or custom metaclass. Example: class MyMetaclass(type): def __new__(cls, name, bases, attrs). Consider complexity trade-offs.
Descriptors define __get__, __set__, __delete__ methods to customize attribute access. Used in properties, methods, class attributes. Enable managed attributes, validation, computed values. Example: property implementation using descriptors. Consider performance implications.
__new__ handles object creation (called before __init__), returns instance. __init__ initializes instance (called after __new__). __new__ used for immutable types, singletons, metaclasses. __init__ can't return value. Consider inheritance implications.
Uses reference counting for basic GC, generational GC for cycles. Reference count tracks object references, frees when zero. Cycle detector identifies and collects unreachable reference cycles. Consider memory management, performance implications.
ABCs define interface through @abstractmethod, can include implementation. Created using abc.ABC. Enforce interface implementation, provide default methods. Unlike Java interfaces, can have implementation. Consider multiple inheritance implications.
Implement __enter__ and __exit__ methods, or use contextlib.contextmanager decorator. Handle resource acquisition/release, exception handling. Consider cleanup guarantees. Example: file handling, database connections.
send() method for two-way communication, throw() for exception injection, close() for generator cleanup. Generator delegation using yield from. Consider coroutine behavior, exception handling. Implement proper cleanup.
Use __getattr__, __setattr__, __getattribute__, __delattr__. Handle attribute lookup, modification, deletion. Consider infinite recursion, performance. Implement proper attribute management. Handle special cases.
MRO determines method lookup order in inheritance. Uses C3 linearization algorithm. Accessible via __mro__ attribute. Handles multiple inheritance, method overriding. Consider inheritance complexity, diamond problem.
Implement __iter__ and __next__ methods for iteration. Consider StopIteration handling. Implement proper cleanup. Handle resource management. Consider memory efficiency. Example: custom sequence types.
__slots__ restricts instance attributes, reduces memory usage. Faster attribute access, prevents dynamic attribute addition. Consider inheritance implications, flexibility trade-offs. Use for memory-critical applications.
Implement rich comparison methods (__eq__, __lt__, etc.). Use @functools.total_ordering for complete ordering. Consider type checking, reflexivity, transitivity. Handle edge cases. Implement proper comparison logic.
Bound methods are instance-specific, include self parameter automatically. Unbound methods are class-level, require explicit instance. Consider method types, descriptor protocol. Handle method binding properly.
Implement __getstate__ and __setstate__ for custom serialization. Handle complex objects, circular references. Consider security implications. Implement proper state management. Handle version compatibility.
Type hints provide static typing information. Used by type checkers (mypy), IDE support. Not enforced at runtime by default. Enhance code readability, maintainability. Consider performance impact, compatibility.
Implement container protocol methods (__len__, __getitem__, etc.). Consider sequence/mapping behavior. Handle iteration, containment checks. Implement proper indexing. Consider memory management.
Class decorators modify/enhance class definitions. Applied using @decorator syntax above class. Can modify class attributes, methods, add functionality. Consider inheritance implications. Handle class modification properly.
Inherit from appropriate exception base class. Implement proper initialization, custom attributes. Consider exception hierarchy. Handle error messages, context. Implement proper cleanup. Document exception conditions.
Protocols define interface behavior without inheritance. Use typing.Protocol for static typing. Support structural subtyping. Consider duck typing implications. Implement protocol compatibility.
Use __slots__, proper data structures, generators. Consider memory profiling, garbage collection. Handle large datasets efficiently. Implement proper cleanup. Monitor memory usage. Consider caching strategies.
Assignment expressions (:=) assign and return value in single expression. Used in while loops, if statements, list comprehensions. Enhances code readability, reduces redundancy. Consider proper usage contexts.
Implement numeric protocol methods (__add__, __mul__, etc.). Handle reverse operations (__radd__, etc.). Consider type coercion, precision. Implement proper arithmetic behavior. Handle special cases.
Generics provide type hints for collections/classes. Use typing.Generic, TypeVar. Support parametric polymorphism. Consider type checking implications. Implement proper type constraints. Handle type variables.
Use @property with caching, implement custom descriptors. Consider computation cost, memory usage. Handle invalidation properly. Implement thread safety. Consider cache management.
@dataclass decorator provides automatic __init__, __repr__, etc. Support inheritance, frozen instances, default values. Consider field options, ordering. Implement custom initialization. Handle field dependencies.
Use decorator pattern, functools.wraps for metadata preservation. Handle argument passing, return values. Consider function attributes. Implement proper wrapping. Handle special methods.
__aiter__, __anext__, __aenter__, __aexit__ for async operations. Support async context managers, iterators. Handle coroutine behavior. Implement proper cleanup. Consider async patterns.
Create descriptor classes with __get__, __set__, __delete__. Handle attribute access, modification. Consider validation, computation. Implement proper state management. Handle inheritance.
Understand object internals, reference counting, memory allocation. Handle weak references, object lifecycle. Consider memory sharing, copy semantics. Implement proper memory management. Handle circular references.