Python Interview Questions
isinstance/issubclass, ABC virtual subclasses, namespace packages, and dynamic/lazy imports.
Ans
isinstance(obj, Type) checks whether an object is an instance of a type or compatible subclass, and it can accept a tuple of types.
Example
pythonvalue = 10 print(isinstance(value, int))
Important Point
Prefer behavior-based design when practical; type checks are useful when an API genuinely depends on type-specific behavior.
Ans
issubclass(A, B) checks whether class A is a subclass of B or B is an appropriate superclass/ABC according to Python's type system.
Example
pythonclass Dog: pass class Puppy(Dog): pass print(issubclass(Puppy, Dog))
Important Point
The first argument must be a class or a TypeError is raised.
Ans
An abstract base class can register an unrelated class as a virtual subclass, allowing certain subclass/instance checks without modifying the registered class's inheritance hierarchy.
Example
pythonfrom abc import ABC class Printable(ABC): pass class Report: pass Printable.register(Report) print(issubclass(Report, Printable))
Important Point
Registration affects ABC checks; it does not add methods to the registered class.
Ans
A namespace package allows portions of one logical package namespace to exist in multiple directories or distributions without a traditional __init__.py in each portion.
Example
textcompany/ tools/ services/
Important Point
Namespace packages are useful for separately distributed components but can complicate packaging if used without a clear need.
Ans
importlib exposes Python's import machinery so applications can import modules dynamically and inspect import behavior.
Example
pythonimport importlib math = importlib.import_module("math") print(math.sqrt(16))
Important Point
Dynamic imports should be controlled carefully when module names come from untrusted input.
Ans
Lazy import delays importing a module or dependency until it is actually needed, which can reduce startup cost in some applications.
Example
pythondef use_json(): import json return json.dumps({"ok": True})
Important Point
Lazy imports can make dependency errors appear later and may complicate startup diagnostics.