Python - isinstance() - Check object type and subclass

Overview of the Python isinstance() Function: Check Object Type and Subclass with Examples

isinstance(object, class) is a built-in Python function that checks if an object is an instance of a specified class or a subclass of that class. It returns a boolean value. True if the object is an instance of the given class or a subclass, and False if it isn't.

The function takes two arguments. The object that we want to check, and the class (or a tuple of classes) to check for. When providing a tuple as a second argument, the syntax looks like that - isinstance(object, (class_A, class_B, ...))

Take a look at the examples below:

Using isinstance() with Custom Classes

class Animal:
    pass

class Mammal(Animal):
    pass

class Reptile(Animal):
    pass

class Dog(Mammal):
    pass

animal = Animal()
mammal = Mammal()
reptile = Reptile()
dog = Dog()

print(isinstance(animal, Animal))          # True
print(isinstance(mammal, Animal))          # True (Mammal is a subclass of Animal)
print(isinstance(reptile, Mammal))         # False
print(isinstance(dog, Mammal))             # True (Dog is a subclass of Mammal)
print(isinstance(dog, (Mammal, Reptile)))  # True (Dog is an instance of Mammal and Mammal is in the tuple)

Output:

True
True
False
True
True

Using isinstance() with Built-In Types

Using isinstance() can be helpful when you want to ensure that an object is of a certain type before performing operations on it.

Remember that isinstance() also works with built-in Python types:

number = 42
text = "Hello, World!"
my_list = [1, 2, 3]

print(isinstance(number, int))           # True
print(isinstance(text, str))             # True
print(isinstance(my_list, list))         # True
print(isinstance(number, (int, float)))  # True (the number is an instance of int, which is in the tuple)

Output:

True
True
True
True

To summarize, isinstance() is a function that allows you to check if an object is an instance of a specific class or a subclass.

Key Points to Remember about the isinstance() Function

• Checks Class Hierarchy: Returns True for both classes and subclasses of the provided type.

• Supports Multiple Types: Use a tuple for checking against multiple classes at once.

• Works with Built-In Types: Handles Python's built-in types like int, str, list, etc.

• Boolean Return: Always returns a True or False value, making it easy to use in conditions.

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