How to Use issubclass in Python: Syntax and Examples

Use issubclass(class, classinfo) to check if class is a subclass of classinfo or a tuple of classes. It returns True if it is, otherwise False.

Syntax

The issubclass() function takes two arguments:

• class: The class you want to check.
• classinfo: A class or a tuple of classes to check against.

It returns True if class is a subclass of classinfo, otherwise False.

python

issubclass(class, classinfo)

Example

This example shows how to use issubclass() to check class inheritance between custom classes and built-in classes.

python

class Animal:
    pass

class Dog(Animal):
    pass

class Cat(Animal):
    pass

print(issubclass(Dog, Animal))  # True because Dog inherits Animal
print(issubclass(Cat, Dog))     # False because Cat does not inherit Dog
print(issubclass(Dog, (Animal, Cat)))  # True because Dog inherits Animal
print(issubclass(int, object))  # True because int inherits object
print(issubclass(str, (int, float)))  # False because str is not subclass of int or float

Output

True
False
True
True
False

Common Pitfalls

Common mistakes when using issubclass() include:

• Passing an instance instead of a class as the first argument causes a TypeError.
• Forgetting that classinfo can be a tuple of classes to check multiple inheritance.
• Assuming issubclass() works with instances instead of classes.

python

class A:
    pass

class B(A):
    pass

obj = B()

# Wrong: passing instance instead of class
try:
    print(issubclass(obj, A))
except TypeError as e:
    print(f"Error: {e}")

# Right: pass class
print(issubclass(B, A))

Output

Error: issubclass() arg 1 must be a class
True

Quick Reference

Usage	Description
issubclass(A, B)	Returns True if A is subclass of B
issubclass(A, (B, C))	Returns True if A is subclass of B or C
issubclass(instance, B)	Raises TypeError, first argument must be a class
issubclass(A, object)	Always True for new-style classes

Key Takeaways

Use issubclass() to check if one class inherits from another.

The first argument must be a class, not an instance.

The second argument can be a class or a tuple of classes.

issubclass() returns True if the first class is a subclass of the second.

Passing an instance instead of a class raises a TypeError.