Code Explanation:
1. Importing Abstract Class Utilities
from abc import ABC, abstractmethod
Imports tools from Python’s abc (Abstract Base Class) module
ABC → base class used to define abstract classes
abstractmethod → decorator to mark methods that must be implemented by subclasses
🔹 2. Defining an Abstract Base Class A
class A(ABC):
A inherits from ABC
This makes A an abstract class
Abstract classes cannot be instantiated directly
🔹 3. Declaring an Abstract Method
@abstractmethod
def f(self): pass
Declares method f() as abstract
pass means no implementation is provided here
Any subclass of A must implement f() to become concrete
📌 This acts like a contract for subclasses.
🔹 4. Defining Subclass B
class B(A):
B inherits from abstract class A
Python checks whether B provides implementations for all abstract methods
🔹 5. Implementing the Abstract Method Using a Lambda
f = lambda self: "OK"
Assigns a function object to the name f
This counts as implementing the abstract method
Equivalent to:
def f(self):
return "OK"
📌 Python does not care about syntax, only that a callable named f exists.
🔹 6. Creating an Object of Class B
B()
Allowed because:
All abstract methods (f) are implemented
B is now a concrete class
🔹 7. Calling the Method
print(B().f())
Execution steps:
B() → creates an instance of B
.f() → calls the lambda function
Lambda returns "OK"
print() displays the result
✅ Final Output
OK
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