Which built-in function can be used to check if an object is an instance of a class or a subclass thereof?

The built-in function isinstance() can be used to check if an object is an instance of a class or a subclass thereof.

Here is how you can use it:

1. Define or identify the object you want to check. For example, let's say we have an object a which is an instance of a class A.

class A:
    pass

a = A()

2. Define or identify the class you want to check against. In our case, it's class A.

3. Use the isinstance() function to check if the object is an instance of the class or its subclass. The function takes two arguments: the object and the class. It returns True if the object is an instance of the class or its subclass, and False otherwise.

print(isinstance(a, A))  # This will return True

4. If you want to check if the object is an instance of a subclass, you can do so by passing the subclass as the second argument to the isinstance() function.

class B(A):
    pass

b = B()

print(isinstance(b, A))  # This will return True because B is a subclass of A

This is how you can use the isinstance() function to check if an object is an instance of a class or a subclass thereof.