Isinstance() Function In Python

# Example Python program that checks 
# an object is of a specific type
class WritingInstrument:
    def write(self):
        print("writing")
    
class FountainPen(WritingInstrument):
    def write(self):
        print("FountainPen writing")

class Pencil(WritingInstrument):        
    def write(self):
        print("Pencil writing")

# Create a FountainPen instance         
pen = FountainPen()
pen.write()

isWriter = isinstance(pen, Pencil)
print("A pen is a pencil:%s"%isWriter)

isWriter = isinstance(pen, FountainPen)
print("A fountain pen is a FountainPen:%s"%isWriter)

isWriter = isinstance(pen, WritingInstrument)
print("A pen is a writing instrument:%s"%isWriter)

FountainPen writing

A pen is a pencil:False

A fountain pen is a FountainPen:True

A pen is a writing instrument:True

class DigitalPen(WritingInstrument):
    def write(self):
        print("Digital pen writing")

digiPen  = DigitalPen() 
isWriter = isinstance(digiPen, (DigitalPen, WritingInstrument))
print("A digital pen is a digital pen and also an writing instrument:%s"%isWriter)

isWriter = isinstance(digiPen, FountainPen)
print("A digital pen is a fountain pen:%s"%isWriter)

A digital pen is a digital pen and also an writing instrument:True

A digital pen is a fountain pen:False

# Example Python program that instantiates a virtual subclass
# and tests whether it is an instance of a virtual base class

from abc import ABC
from abc import abstractmethod

# WritingInstrument interface 
class WritingInstrument(ABC):
    @abstractmethod
    def write(self):
        pass

# Independent DeviceSpecificStylus not implementing the 
# interface WritingInstrument 
class DeviceSpecificStylus:
    def write(self):
        print("DeviceSpecificStylus moving")

# Developer decides DeviceSpecificStylus is a perfect
# WritingInstrument and registers it with the WritingInstrument
# hierarchy
WritingInstrument.register(DeviceSpecificStylus)

stylus = DeviceSpecificStylus()
isWriter = isinstance(stylus, WritingInstrument)
print("stylus is an instance of WritingInstrument: %s"%isWriter)
 

stylus is an instance of WritingInstrument: True

class MechanicalPencil(Pencil):
    def write(self):
        print("Mechanical pencil writing")

mechPencil = MechanicalPencil()
print("mechPencil is an instance of WritingInstrument:%s"%isinstance(mechPencil, WritingInstrument))

A digital pen is a fountain pen:False

mechPencil is an instance of WritingInstrument:True